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LIBRARY OF CONGRESS, 



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Chap. _t* Copyright No... 

Shelf_jWlSL.S 



UNITED STATES OF AMERICA. 



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Price One Dollar. 



Vitrified 

Paving Brick 

A Review of Present Practice in the Manufac 
ture, Testing and Uses of Vitrified 
Paving Brick. 




BY 



H. A. WHEELER, E. M., 

Clay Specialist of the Missouri Geological Survey. 





INDIANAPOLIS, IND.: 
T. A. RANDALL & CO., PUBLISHERS. 
1895. 



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COT 12 1895 



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COPYRIGHTED, 

1895, 

BY T, A. RANDALL & (X). 



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^PREFACE. 



The following contribution to the literature of paving brick 
Is the result of studies by the writer covering the past eight 
years. During this period the paving brick industry has had a 
phenomenal development, as from a scarcely known article 
that was used in but a few towns, and looked upon with much 
suspicion, it is now used by nearly all the cities and large 
towns in this country. It has not only won its recognition as a 
standard article for street paving, but is found to be even 
more reliable than most materials used for this purpose, when 
surrounded by the safeguards required in municipal engineer- 
ing. As the industry is still in the infancy of its development, 
the merits of vitrified brick are not yet as widely. known as it 
deserves, and this contribution is offered as a review of the 
present practice, which has considerably advanced since the 
publication of Prof. Ira Baker's valuable pioneer brochure in 
1891 ("Brick Pavements"). Mr. C. P. Chase also published a 
similar paper in 1891 ("Brick Pavement"), which is mainly 
written for the city engineer. Mr. M. D. Burke published a 
valuable contribution in 1892, which is based on tests made at 
Cincinnati, and contains many pungent remarks that are es- 
pecially interesting to the municipal engineer. 

"The Clayworker" (Indianapolis, monthly,) republished in 



VITRIFIED PAVING BRICK. 



December, 1893, Mead's excellent article before the Chicago 
Engineering Congress, and is now bringing out a new series 
of articles by him on nitrified brick. This artistic monthly is 
also very prolific in articles and discussions on paving brick 
from many sources, and at present is bringing out a very valu- 
able series of papers from the able pen of Prof. Orton, Jr. 
"Engineering News" (New York, weekly,) has published many 
tests on paving brick during the past six years. 

The writer herewith begs to express bis thanks for the 
courtesy extended to him by the many city engineers who 
favored him with their personal experience with brick pave- 
ments. H. A. WHEELER. 

St. Louis, July 18, 1895. 



CONTENTS. 



PAGE 

History of Paving Brick 7 

Definition of Vitrified Brick 11 

Clays Employed 14 

Composition of Paving Brick Shales 18 

Physical Property of Clays 21 

Manufacture of Paving Brick 24 

Winning . - 24 

Crushing 26 

Screening 26 

Pugging 27 

Molding 27 

Repressing 30 

Drying 31 

Burning 31 

Physical Qualities of Paving Brick 36 

Color 36 

Structure 37 

Hardness 38 

Porosity 39 

Density 41 

Crushing Strength 42 

Cross-Breaking Strength 43 

Toughness 44 



VITRIFIED PAVING BRICK. 



Method of Testing Paving Brick 46 

Eye Examination 46 

Laboratory Tests 48 

Density 48 

Absorption 49 

Crushing Strength 53 

Cross-Breaking Strength 54 

Hardness 55 

Rattler Test 56 

Evaluation of the Results 59 

Uniformity of Results . 64 

Value of the Rating Formula 66 

Uses of Vitrified Brick 69 

Sewers 69 

Foundations 70 

Sidewalks 70 

Street Paving 71 

Comparison of Street Paving Materials 71 

First Cost. 71 

Maintenance 72 

Traction 72 

Footing ... 72 

Durability 73 

Cleanliness 73 

Repairs 73 

Health 73 

Noise 74 

Size of Brick 74 

Foundations for Paving Brick 76 

Durability of Paving Brick 77 

Cost of Paving Brick 83 



HISTORY OF PAVING BRICK. 



Brick for street paving has been in use for more than a 
century in Holland, where the absence of natural paving ma- 
terial developed a very durable quality of paving brick by* 
mixing the fine river silt or mud with sand. The village of 
Moor, on the river Yssel, is especially famous for the excel- 
lence of its brick and the magnitude of its paving-brick in- 
dustry. 

To a much less extent, and for a shorter period, they have 
been used in northern England, especially in Staffordshire and 
Leeds, under the name of "blue brick" and "terro-metallic 
ware," where their application is restricted more to stables, 
chemical works and similar places where a non-absorbent brick 
is desired. Where the clay is not readily fusible, slag, or mill 
cinder, or chalk dust is added in English practice, to secure the 
fluxing or vitrification that is so essential in this class of brick. 

Paving brick was first used in the United States at 
Charleston, W. Va., in 1870, a town of 12,000, where a small 
section was laid as an experiment. This proving satisfactory, 



Development 
Abroad. 



Development 
in the United 
States. 



VITRIFIED PAVING BRICK. 



a block of one of their principal streets was paved in 1873, in 
grading for which it was necessary to take up the small sec- 
tion laid in 1870. This is still in use, although laid on a very 
poor foundation or boards, and though the street has been re- 
peatedly torn up for laying pipe, etc., it is still in fair condi- 
tion. Samples of this brick kindly sent to me by the city en- 
gineer, M. W. A. Hogue, show it to be a side-cut repressed 
hard-burned building brick of high density, or 2.48, that ab- 
sorbs 4.5 per cent of moisture in a twenty-four-hour test, and 
indicates a wear of one-quarter to one-half inch after twenty- 
two years' service. 

Bloomington, 111., a town of 26,000, put down paving brick 
in 1875, which, after twenty years' service on one of their 
principal streets, is being replaced this year by shale pavers. 
A sample courteously forwarded to me by Mr. W. P. Butler, 
the city engineer, shows that a very poor glacial clay was used 
(much inferior to the Charleston clay), and the brick was made 
by the "slop" process, or from a very soft mud, by hand, with 
out repressing. It shows an absorption of 4.33 per cent, water 
after twenty-four hours soaking, and a wear of one to one 
and a half inch, while it has a density of 2.11, or is very low. 

St. Louis, in 1880, put down three trial lots of brick pav- 
ing, one of which was the result of experiments dating back 
to 1873, the Sattler brick. These all proved failures, from 
being too soft or too brittle, and were all laid on bad founda- 
tions. Another lot of the Sattler brick was tried in 1881, which 
was successful, but the maker was unable to furnish a uni- 
form, reliable brick, as he was experimenting with a fire clay 



VITRIFIED PAVING BRICK. 



that was too refractory and very difficult to handle without 
cracking. This made such a deep impression on the City 
Fathers, though made in the infancy of the industry, when no 
first-class pavers had yet been made in this country, that 
paving brick only received official recognition again this year, 
though it now promises to become the leading pavement of 
this Western metropolis, with its population of over 600,000. 

Wheeling, W. Va., put down an impure fire clay paving 
brick in 1883 that was quite successful, and this was the fore- 
runner of the paving brick industry, as it was the first to 
inspire confidence. 

Decatur, 111., also put down a vitrified brick this same 
year that was made from a glacial clay, which is still in ex- 
cellent condition. 

Galesburg, 111., the home of the shale brick, laid the 
first shale paver in 1884, on their principal street, where it is 
still doing excellent service. 

1885 saw the first encouraging use of vitrified brick, as 
during this year it was laid in Columbus, Zanesville and Steu- 
benville, O., and Peoria, 111. Since then its use has steadily 
grown, at first slowly, as its merits were cautiously investi- 
gated, but as the accumulated experience grew more and more 
favorable, its adoption became more general, until now it is 
in use in nearly four hundred cities and towns in this country. 

Although Philadelphia adopted brick for its residence streets 
in 1888, the large cities, with their characteristic conservatism, 
have been slow in using this new paving material: but with 



10 



VITRIFIED PAVING BRICK. 



Popularity of 
Brick Pave= 

merits. 



its adoption this year (1895) by New York, Chicago, St. Louis* 
and Pittsburg, it is now in use in all the large cities, and the 
early prejudice against it as a nonenduring, unreliable pave- 
ment has given way before the overwhelming accumulation 
of discriminating evidence. 

To show the growing popularity of this excellent, econom- 
ical pavement, a canvass was made in 1894 by "Paving and 
Municipal Engineering" of the projected street improvements 
for that year in thirty-two cities. A summary of the returns 
showed that 44 per cent, of the new pavement was to be brick, 
32 per cent, macadam and 24 per cent, asphalt, showing al- 
ready a strong lead over its two great rivals— the former in 
cheapness and the latter in smoothness. 

While brick has thus far been mainly restricted to residence 
streets or alleys in the large cities, where the traffic is not 
heavy, it has been subjected to very severe wear in some of 
the smaller cities with very satisfactory results, and in view of 
the marked improvement in quality that has been made 
within the past five years, and the still greater improvements 
that are in sight, the future will undoubtedly see brick success- 
fully used for the severest traffic of our largest cities. For 
while it will never be profitable to attempt to make brick as 
durable as granite, it is so much cheaper, the traction is so 
much easier, the noise so much less, and it is so much cleaner, 
that it will win a popularity, when better known in our large 



*St. Louis will use vitrified brick on thirty-five alleys and 
fourteen streets in 1895, as an initiatory introduction, while Chi- 
cago is contemplating laying sixty miles of brick pavements. 



VITRIFIED PAVING BRICK. 



11 



cities, that will cause it to largely replace granite, even if it 
has to be renewed more frequently. 

From an humble beginning, in which the making of paving 
brick was a side issue in a few village brickyards and fire- 
brick factories, the manufacture of paving brick as a distinct 
industry began about ten years ago, and the giant strides it is 
now making date within the past five years. It is utilizing a 
class of clays that has hitherto been almost completely neg- 
lected (the shales), and has erected plants which for magnitude 
of output, capital invested and general design are a decided 
advance in the clay industry. There are now over 175 plants 
devoted to this specialty in this country, with individual out- 
puts as great as 60,000,000 to 100,000,000 per annum, and 
capital investments as large as $500,000 to $1,000,000 per com- 
pany. 

DEFINITION OF THE TERM VITRIFIED BRICK. 

There is a misconception among some engineers and brick- 
makers as to the definition of vitrified brick, as unless a brick 
shows a decidedly glasslike fracture, they refuse to call it 
vitrified, and even condemn brick from lack of such glassiness 
that are not infrequently the toughest and most durable of 
pavers (brick with a stonelike fracture). They quote Webster 
to substantiate their claims, thereby failing to discriminate be- 
tween a popular definition and a technical or special use of 
the term. The No. 1 pavers that are at present on the market, 
whether made from impure fire clay or shale, are nearly al- 
ways vitrified, though much more thoroughly vitrified in the 
latter case. 



Developement 
of the Indus= 
try. 



flisconception 
of the Term. 



12 



VITRIFIED PAYING BRICK. 



Study of the 

changes in a 

Clay. 



Point of Incipi* 

ent Vitrifica= 

tion. 



Viscous Vitri= 
fication. 



To properly appreciate the correct use of the technical term 
of vitrified brick, it is desirable to look at the change that 
occurs in paving clays in passing from the condition of a mud 
to a distinctly glassy mass. A plastic clay, when mixed with 
a proper amount of water, makes a mud or paste that can be 
readily molded, and yet is tenacious enough to retain the shape 
given to it in molding, if carefully handled. On drying off the 
mechanically admixed water that rendered it plastic, it shrinks 
2 to 11 per cent, to a firm, earthy mass that bears handling, 
though it is so soft as to be easily scratched by the finger-nail, 
and the individual particles of clay are easily distinguished. 
On heating the dry clay to a red heat (or about 1200 degrees 
P.), the chemically combined water is driven off, which renders 
the clay non-plastic, it again begins to shrink and to grow 
harder and stronger as the heat is raised above redness, but 
the individual particles of clay are still easily recognized, and 
the clay is very porous. When the heat is further raised to 
about a bright cherry heat (or from 1500 to 1800 degrees F.), 
depending on the particular clay, it shrinks an additional 1 to 
10 per cent., it is very much stronger, much less porous, has 
acquired the hardness of tempered steel, and the individual 
particles are no longer recognizable. This point, which is quite 
well defined, I have called the point of incipient vitrification; 
from thence to the stage of a molten mass there is no longer 
any sharp line of demarkation. as it imperceptibly becomes 
more and more vitreous, and gradually begins to soften and 
change its shape, especially under pressure. It finally becomes 
a very viscous semi-liquid, and when chilled and broken pre- 
sents a thoroughly glassy appearance. 



rification. 



VITRIFIED PAVING BRICK. 13 

From the point at which the clay particles have sufficiently 
coalesced that they can be no longer recognized, or the point 
of incipient vitrification, to the point of viscous liquidity, re- 
quires an increase in temperature of 100 to 600 degrees F., 
depending on the kind of clay, and is usually 400 degrees in 
the clays suitable for paving brick. Midway between these 
two points the clay ceases to be porous and stops shrinking; .?. m .. e 
it has attained its maximum hardness, or scratches quartz; it 
has a maximum toughness and cross-breaking strength if 
slowly cooled, and the fracture shows complete coalescence of 
the particles, or it is completely vitrified, though the shape is 
retained if not subject to pressure. This stage, though not 
sharply defined. I have called the point of complete vitrifica- 
tion, and though difficult to describe, it is quickly and easily 
recognized by the trained eye. It is the stage that clay should 
be brought to in order to make an ideal paving brick. If 
heated higher, there is a slight loss in hardness, a much greater 
risk of brittleness, and a marked tendency to be distorted from 
incipient flow, though the fracture is more decidedly glassy; 
yet this advanced stage is what some think a brick should be 
brought to in order to be called vitrified from Webster's point 
of view. 

Salmon brick, having only been exposed to a red heat, 
are extremely porous, or absorb from 15 to 30 per cent, of 
water; they are very soft, or from 2.5 to 3.0 in hardness, 
and are in the initial stage of shrinking, hardening and 
strengthening. 

Hard building brick, having been raised to a cherry 



14 VITRIFIED PAVING BRICK. 

red heat, are less porous, or absorb, from 6 to 15 per cent, of 
water; they are much harder, or from 4.5 to 5.5 in hardness; 
are much stronger, and while showing considerable shrink- 
age, the distinct grains of the clay are still evident. 

Fire clay paving brick usually exhibit a homogeneous, 
compact, dense body, in which the grains of clay can no 
longer be discerned, or have reached the stage of incipient 
vitrification; they are slightly porous, or absorb from 3 to 
6 per cent, of moisture; they are very hard, being able to 
scratch glass or steel, or are 6.0 to 6.5 in hardness, and are 
very tough and strong. They are sufficiently dense and strong 
to successfully withstand frost, and are hard and tough enough 
to wear well under moderate traffic. 

Hard-burned shale brick usually exhibit a very dense, 
thoroughly homogeneous, compact body that shows com- 
plete vitrification; they are practically Don-porous, or absorb 
from to 2 per cent, of moisture; they are extremely hard, 
being able to scratch quartz; and are very strong and tough, 
and pre-eminently adapted for street paving, if slowly cooled. 

The salmon and building brick are too soft, too porous and 
too weak for street paving purposes; the two latter are both 
suitable for pavers, and are vitrified, but the important dis- 
tinction should be made that one is only incipiently or slightly 
vitrified, while the other is completely or thoroughly vitrified. 

CLAYS EMPLOYED. 

Three distinct classes of clays are employed for the manu- 
facture of paving brick, to-wit: 



VITRIFIED PAVING BRICK. 15 

I. Surface clays, as the drift, loess and residual clays. 

II. Impure fire and potters' clays. 

III. Shales. 

I. SURFACE CLAYS.— The surface clays are seldom suit- 
able for pavers, though almost exclusively used for builders, 
as they are usually so siliceous, or 60 to 80 per cent, in silica, 
and occasionally so very calcarous, or 10 to 25 per cent, of 
lime, that it is practically impossible to vitrify a large per- 
centage without losing their shape. For the range in temper- 
ature between the points of incipient and viscous vitrification 
in such clays is so small as to require a perfection in the control 
of the kiln that is beyond present attainments. While the 
earliest pavers, or those of Charleston, W. Va., and Blooming- 
ton, 111., were made from such clays, they were not vitrified, 
but only hard-burned builders, and their endurance was due 
to the light traffic of a small town rather than to superior 
quality, and in each case they have given way to shale brick. 
In a few cases* these surface clays have a composition that is 



*As at Decatur, 111., and Huntington, W. Va. The Hunting- 
ton clay is a very plastic, tough, safe working clay, standing 
rapid drying and firing, and is very fine-grained. It gives the 
following analysis, per Mr. Otto Rissmann, of the St. Louis 
Sampling and Testing Works: 

Per cent. 

Silica 57.04 

Alumina 18.26 

Sesquioxide of iron 6.38 

Lime 2.41 

Magnesia 1.98 

Ignition loss 10.16 

Total 96.23 



16 VITRIFIED PAVING BRICK. 

favorable for successfully burning a large percentage into 
hard, tongh brick, but these are the exception, and present ex- 
perience does not indicate that it will pay to add the mixtures 
necessary to convert them into a good paving material, as is 
done in Holland, in competition with the large bodies of shales 
that are naturally so favorably constituted for making a cheap 
and superior quality of paving brick. 

II. IMPURE FIRE and POTTERS' CLAYS.— In point of 
history the impure fire clays* were next used for making pav- 
ing brick, and for some time were exclusively employed in the 
extensive Upper Ohio district; but though still largely used, 
they are slowly yielding to the cheaper and more durable shale 
clays. A pure fire clay, on account of its infusibility, or the 
inability to vitrify it, is a very unsatisfactory clay to use for 
paving brick, as it is too porous, lacks hardness and strength, 
and is too expensive to burn; but if quite impure, it can be 
burned to incipient vitrification, when it becomes much denser, 
harder and stronger, and makes a very fair quality of paving 
brick. It possesses the advantage of being impossible to 
overburn, a point that must be carefully watched with 
shales or surface clays. For this reason the fire clay brick are 
less likely to be brittle than shale brick, but they are always 
more porous, or absorb from 2.5 to 7.0 per cent, moisture, 
though they usually successfully withstand the frost, in spite 
of this porosity, notwithstanding theoretical opinions of en- 
gineers to the contrary. Brick made from fire or potters' clay 
are apt to be light-colored, or cream to buff, from the small 



*Also known as "bastard fire clay," pipe clay. etc. 



VITRIFIED PAVING BRICK. 17 

amount of iron such clays usually contain, and the latter, being 
generally in the condition of disseminated grains of pyrite or 
limonite. gives a brown or black-speckled appearance to the 
light ground mass. The fluxing impurities should exceed 5 
per cent, in a fine-grained fire or potters' clay, or 7 per cent. 
In a coarse-grained clay, to make it fusible enough for paving 
purposes, and the greater the amount of the fluxing impuri- 
ties the cheaper it can be burned., and the denser, harder 
and stronger will be the resultant brick, from the more thorough 
cementation of the clay particles by the fluxing action of these 
Impurities. The fluxing impurities which render a clay fusible 
are iron, lime, magnesia and the alkalies, potash and soda; 
while the finer the grain and the less dense a clay, the more 
fusible it is, other things being equal. 

III. SHALES.*— The material from which most of the pav- 
ing brick is now made, and which is usually found in very 
much larger bodies than either surface clays or fire clays, is 
the impure, hard, laminated clay that is known as shale by the 
geologists. Though only recently used for this purpose, and 
apparently possessing no plasticity as it lays in thick stratified 
t)eds, it is found to readily work up into a plastic magma when 
ground, and to usually have the very impure composition that 
is so desirable for vitrified brick. This very impure nature is 
the secret of the success of shales for this purpose, if the phys- 



* Shales are incorrectly called soapstone or soaprock by coal 
miners, from which they radically differ in every respect; 
they are also frequently but erroneously called slate by en- 
gineers, from which they differ but slightly in origin and com- 
position, but the slates cannot be rendered plastic. 



18 VITRIFIED PAYING BRICK. 

i 



ical properties are favorable, and consequently there is a great 
range in the composition of paving brick shales. Usually they 
range between the limits given in the following table, which is 
compiled from the analyses of twenty-five carefully collected 
samples of Missouri paving brick shales that were made by the 
Missouri Geological Survey, and twenty-five from the principal 
paving brick centers of the United States, collected from, 
various sources: 

COMPOSITION OF PAVING-BRICK SHALES. 

(Deduced from fifty reliable sources.*) 

Minimum. Maximum. Average^ 

Per cent. Per cent. Per cent. 

Silica (Si02) 49.0 75.0 56.0 

Alumina (A1203) 11.0 25.0 22.5 

Ignition loss (mainlv IPO)** 3.0 13.0 7.0- 

Moisture (H20) 0.5 3.0 1.5 

Total nonfluxing constituents 87.0 

Sesquioxide of iron (Fe203) 2.0 9.0 6.7 

Lime (CaO) 0.2 3.5 1.2 

Magnesia (MgO) 0.1 3.0 1.4 

Alkalies (K20, Na20) 1.0 5.5 3.7 

Total fluxing constituents , 13.0 

Grand total 100.0 

*There are manj^ analyses in the current literature that pur- 
port to be of paving brick clays and shales which differ greatly 
from the above, but the writer has found them to be misap- 
plied analyses of burned bricks, kaolins, fire clays or other 
material not used for paving brick. 

**Ignition loss includes sulphur (S), carbonic acid (C02) and 
combined Avater (H20), though mainly the latter. 



VITRIFIED PAVING BRICK. 19 

While this range in composition is large, the well-known 
paving brick* are made from shales that agree quite closely 
with the average analysis given above, especially in the fluxing 
constituents, so that this will be a valuable guide as a desir- 
able but by no means necessary composition for a good paving 
brick clay. A specific analysis is herewith given (from Orton) 
of one of the best-known shales in the country with regard to 
the high quality of the brick made therefrom, or the Canton, 
Ohio, shale (Royal Brick Co.): 

ANALYSIS OF CANTON (O.) SHALE. 

Per cent. 

Silica 57.10 

Alumina 21.29 Nonfiuxing constituents, 

Combined water 6.00 85.69 per cent. 

Moisture 1.30 

Sesquioxide of iron 7.31 

Lime 0.29 Fluxing constituents, 

Magnesia 1.53 13.18 per cent. 

Alkalies 4.05 

Total 98.87 

An important matter in the composition of shales is the con- 
dition of the iron, which the chemist almost invariably de- ^° n ^ lt,on of 
termines as and reports in the form of the higher or sesqui- 
oxide. In many cases it exists in the condition of the lower or 
protoxide, and more frequently it is a mixture of both the high- 
er and lower oxide, as there is scarcely a shale bank without 

*As Moberly, Kansas City, and St. Louis, Mo.; Leaven- 
worth. Kan.; DesMoines, la.; Galesburg and Streator, 111.; and 
Columbus, Zanesville, Akron and Canton, O. 



the Iron. 



20 



VITRIFIED PAVING BRICK. 



Influence of 
Lime. 



Fire Clay ilix= 
tures. 



concretions of siderite or ferrous carbonate. Now it is a very 
vital matter in the successful burning of the shale as to the con- 
dition of the iron, and more than one good shale has been con- 
demned from want of knowledge of this- fact, and the inability 
to properly manage it in the burning, as there is a marked 
difference (over 200 degrees F.) in the fusibility, according to 
the condition of the oxidation of the iron. It is also very de- 
sirable that the iron be uniformly diffused through the clay, 
to get the best results; for if present as crystals, concretions or 
seams, it gives a mottled or spotted appearance, and produce's 
local vitrification in spots. 

Another matter that is frequently misunderstood, and faulty 
decisions made in consequence, is the influence of lime on 
clays in general. If the lime is present in the form of feld- 
spar (or as a silicate) it is a very valuable flux, and the more 
the better; but if present in the form of carbonate, it will 
not make a strong brick if in large amounts, and the color 
will be cream to buff, no matter how much iron* may be pres- 
ent, if the lime is uniformly diffused through the clay. If pres- 
ent as concretions, pebbles or veinlets, and not finely ground, 
the quicklime resulting from the burning is liable to cause 
swelling or cracking when the burnt ware is soaked in water. 
The failure to discriminate as to the condition of the lime has 
resulted in frequent sweeping statements condemning lime 
under all circumstances. 

When shales are too fusible, fire clay is sometimes added to 



*Iron is almost invariably the coloring agent in aU naturally 
colored brick. 



VITRIFIED PAYING BRICK. 



21 



the extent of 10 to 25 per cent., as at Zanesville, O., and Des 
Moines, la., to ''stiffen it," or make it stand up better in the 
kiln, with satisfactory results. 

PHYSICAL PROPERTIES OF CLAYS. 

The chemical discussion of clays has been hastily passed 
over, on -which alone a volume could be written. For no mat- 
ter how carefully a clay has been sampled and analyzed, 
and though one possesses the rarely executed proximate as 
well as the ultimate analysis, the merits of a clay can never 
be decided upon from only a chemical analysis; it is 
of much assistance in forming an idea about a clay, and 
within certain limts will enable one to condemn, but never 
indorse a clay. Before one can safely pass judgment on a 
clay for any purpose, a thorough physical examination is 
necessary, which gives the information how to work the 
clay, and the kind and cost of the ware that can be made 
from it. Such a series of physical tests comprise the deter- 
mination of the 



Limited value 
of Chemical 
Analysis. 



1. 

o 
•J. 

4. 

5. 
<». 

7. 

8. 



PHYSICAL FACTORS OF CLAYS. 

Plasticity. 

Water required to make a plastic paste. 

Shrinkage in drying. 

Shrinkage in burning. 

Speed in drying. 

Speed in burning. 

Point of incipient vitrification. 

Point of complete vitrification. 



22 



VITRIFIED PAVING BRICK. 



Plasticity. 



Shrinkage. 



Drying. 



9. Point of viscous vitrification. 

10. Density before and after burning. 

11. Colors of the burned ware. 

12. Strength of the burned ware. 

All of these factors have an important bearing on either 
the manufacture or use of the ware, yet barring the ques- 
tion of fusibility and color, and then only imperfectly, a 
chemical analysis gives no clew whatever on these indis- 
pensable points. 

The plasticity is pre-eminently the first question in any 
clay, as on this property depends the ability to mold the 
ware. If too lean to be readily or safely molded, it requires 
admixture with a "fat," or plastic, or "bond" clay, while 
if too "fat" or plastic, it needs reducing with sand, "grog," 
or a lean clay. The plasticity is of special importance in 
paving brick, as if too plastic, the laminations, which have a 
weakening effect on the brick, are excessively developed. 

The shrinkage determines how much larger the molds and 
dies have to be made to produce a given size of brick, the 
amount of settle in the kiln, and whether "grog" is neces- 
sary to reduce the shrinkage if excessive; the total shrinkage 
varies from 1 to 15 per cent , and usually fluctuates from 8 to 
12 per cent. 

The speed of drying determines the care with which a 
clay must be dried, and the size and capacity of the diying 
chambers. Some lean clays can be dried in twenty hours 
without checking (small cracks), while some strong clays re- 
quire three to five times as much time in order to dry with- 
out cracking. 



VITRIFIED PAVING BRICK. 



The speed in burning is a peculiar property that enables 
some clays to be rapidly heated without cracking, while 
others have to be very slowly fired; this will greatly influ- 
ence the mode of handling the kiln, and also the number of 
Jkilns required to furnish a given output. 

The points of incipient, complete and viscous vitrification 
.are very important in all clays, as it is necessary to attain 
the first to develop strength, while with pavers it is not only 
of vital importance to readily attain the second, but there 
must be a wide margin each side of the point of complete 
vitrification to enable the kiln burner to produce a large per- 
centage of No. 1 brick. For if this margin is small, there will 
oe a heavy loss from either overburned, misshapen brick, or 
from soft, underburned brick. 

The density of the burned ware is very uncertain until 
tested, as some clays give a spongy, porous, light body when 
vitrified, while others give a close, dense, uniform, stone-like 
oody, which latter is absolutely necessary in paving brick. 

The color of the burned clay is a vital matter with most 
clay ware, and is of great assistance in paving brick in check- 
ing the work of the burner, after once being familiar with the 
colors of a given clay at different heats. 

The strength of the burned ware is the crucial test of a 
paving brick, as on this question hangs its durability, and 
many clays that are satisfactory up to this point fail at the 
severe demands required for a durable paver. In fact the 
majority of shales and impure fire clays cannot be used for 
pavers, because lacking the great toughness that is required 
of a paving brick. 



Burning. 



Density. 



Color. 



Strength, 



24 



VITRIFIED PAVING BRICK. 



MANUFACTURE OF PAVING BRICK. 



Surface Clays. 



Fire Clays. 



Shales. 



Steam Shovels 



WINNING THE CLAY.— As the surface clays are now 
rarely used for paving brick, the usual methods of handling 
such clays are seldom used, or the pick and shovel, plow 
and scraper or cart, disc cutter and automatic clay gatherer,, 
according to the size of the yard and haul. Nor are paving 
brick clays weathered, a process which increases the plas- 
ticity and homogenity, though at the expense of extra han- 
dling, loss of time and the locking up of considerable capi- 
tal; for while this process improves the clays, competition- 
has now forced this to be regarded as a luxury. 

The impure fire clays are usually mined by the room and 
pillar system, like coal, with which they are usually asso- 
ciated and much resemble in their mode of occurrence and 
method of handling. Like coal, they are also worked by- 
driving and drawing, or running entries out to the boundary,, 
and then drawing the pillar back to the shaft or adit. 

The shales are usually worked in open pits, after strip- 
ping off any superficial surface clays, and are either worked. 
by blasting, or else handled from the solid bank into the car 
by a steam shovel. 

If the plant is large enough to keep a steam shovel mod- 
erately busy, it is the cheapest and best way of working, 
as a better mixing is obtained by the rubbing of the nose of 
the shovel up the face of the bank, and as the face is kept 
vertical, there is much less delay and trouble in rainy 
weather by the shale not getting very wet. The depth of a 
steam shovel cut is limited to about twenty feet, however, 



VITRIFIED PAYING BRICK. 25 

vhereas there is no limit in blasting, and faces eighty feet 
high are so worked at Galesburg, 111., and Des Moines, la. 
By putting a one to one-and-a-half -yard shovel on a two-and- 
a-half-yard machine, steam shovels have been able to 
successfully rip up very hard, tough shales, as at Alton 
and Galesburg, 111., and Des Moines, la., though not without 
break-downs that are still too frequent, and further improve- 
ments are needed in strengthening the weak points of these 
valuable machines. By loosening the bank with dynamite, the 
work can be made much easier and very much less severe on 
the steam shovel, but much of its economy is lost when nitro- 
glycerine supplies the energy instead of coal; and if the points 
of the shovel are kept sharp, they have proved their ability to 
tear up very tough shales without assistance. If a yard is 
making less than 50,000 brick a day, there is usually no econ- 
omy in a steam shovel, as the shovel crew is idle about 70 per 
cent, of the time, and a daily output of 200,000 is necessary to 
keep the shovel constantly at work. 

From the bank or pit to the factory, the clay or shale is usu- 
ally hauled in either side-dumping or drop-bottom cars, by horse, 
locomotive or wire rope, and ingenious devices have been in- 
troduced for coupling, dumping and latching automatically. 
Occasionally long belt conveyors transfer the clay from the 
pit to the crushing floor, but this is usually confined to small 
plants. For large plants exhaust the clay at the rate of one- 
half to three acres per year, depending on the thickness of 
the deposit, as two cubic yards or more are needed per 1,000 
brick. 



Cars. 



26 VITRIFIED PAVING BRICK. 

CRUSHING.— Shale is nearly always crushed in dry pans 
or Chilian mills, with solid mullers or rolls that are usually 
four feet diameter and twelve inches wide, and which run 
within a revolving pan nine feet in diameter, with a grated 
bottom. A pair of such pans can usually supply the largest 
size brick machine, and they have proved very satisfactory, 
as they crush from five to ten cubic yards of shale per pan per 
hour. Rolls and centrifugal disintegrators are occasionally 
used, but they are not satisfactory on most shales, which are 
usually too tough to be cheaply crushed fine by this system, 
though it is very efficient on surface clays. 

SCREENING.— From the dry pan the crushed shale should 
go to screens, and both fixed and shaking riddles, and re- 
volving trommels are employed. They all require the use 
of knockers, to prevent sticking of the wet clay, and at many 
plants a boy is also needed, to keep the screens from clog- 
ging. The trommels and shaking screens are more compact 
than the fixed riddle, but the latter is simpler to clean and 
repair. In some of the older plants the sizing accomplished 
by the gratings of the dry pans is regarded as sufficient, and 
no screens are employed, but this is a serious mistake as it 
reduces the capacity of the pan, and causes very imperfect 
crushing, from the wear and breakage of the bridges of the 
gratings. As the finer the clay is crushed the stronger the re- 
sulting brick, these coarse particles produce an inferior, un- 
homogeneous product. In fact most plants are still faulty in not 
screening fine enough, as four to eight-mesh screens are em- 



VITRIFIED PAVING BRICK. 27 

ployed, whereas ten to sixteen meshes per linear inch should 
be used, to give the best results. 

PUGGING.— The crushed clay or shale is next mixed and 
worked with water into a plastic mass by the pug mill, which 
is a long trough containing a series of wide blades set with a 
coarse pitch on a heavy shaft. This pugging or tempering 
should be thoroughly done, to remove air inclosures, secure a 
homogeneous mixture, and reduce the laminations in molding 
to a minimum; but most pug mills are too short to properly 
accomplish this, or only six to nine feet long (along the blades), 
or are pitched too rapidly, and are the cause of many defects 
in the brick. They should be at least ten to twelve feet long, 
and have the blades or knives 90 degrees apart. Fire clays are 
often pugged or tempered in "wet pans" or "chasers," which 
are small Chilian mills with a solid bottom, while the mullers 
have a narrow tread. The clay is both crushed and tempered or 
worked into a homogeneous paste in this pan, being kept in it 
until thoroughly ground and tempered. The wet pan yields a 
superior product to the pug mill, as it can be retained indefi- 
nitely in the pan, or until thoroughly tempered; but as it re- 
quires a larger plant, and takes more labor and power, it is 
not usually used for paving brick, though in quite universal 
use for fire brick, sewer pipe, terra cotta, etc. 

MOLDING.— Paving brick are made by the stiff mud 
process, except in a few small yards which still retain the 
old-fashioned soft mud and repressing system, and these 
have proved the only satisfactory methods of making a reason- 
ably large percentage of good pavers. Numerous attempts 



28 



VITRIFIED PAYING BRICK. 



Failure of Dry 
Press Process. 



Strength of 
Dry Hud. 



Stiff Hud 
Machines. 



have been made to use the semi-dry or dry press methods, 
which are in such successful use for building brick, especially 
about St. Louis, but they have failed to produce more than a 
small percentage of good pavers. For in the press systems 
there is no bond between the clay particles, and they merely 
cohere as the result of the quickly-applied pressure, and unless 
such brick are burned to complete vitrification, they fail to 
give a solid, strong, non-porous brick. 

To show the strength of the natural bond of the clay parti- 
cles when worked by the mud process, it was found in testing 
about two hundred samples of Missouri clays and shales, that 
the dry mud (before burning) had a tensile strength of 50 to 
300 pounds to the square inch, averaging about 150, and the 
gumbo clays ranged from 300 to 400 pounds, or were much 
stronger than the natural cements. 

The type of machine used for the stiff mud process is usu- 
ally a continuous-working auger that forces the tempered clay 
or mud through a forming die; this gives a continuous bar of 
stiff clay, which passes under an automatic cutter that cuts it 
into the desired size. As the bar leaves the die, it is usually 
sanded, to prevent the bricks from sticking together in the 
kiln. Instead of an auger, producing a continuous stream of 
clay, reciprocating plungers are sometimes employed, which 
give an intermittent bar, and occasionally steam cylinders with 
clay plungers are used, similar to sewer pipe presses. The 
first method is the cheapest, and this style of machine has been 
developed to a producing capacity of 12,000 bricks an hour, or 
100,000 per day. Formerly the dies were made about 4%x2% 



Side Cut. 



VITRIFIED PAVING BRICI\. 29 

inches in size, producing- an end-cut brick, but of late 9x4^- 
inch dies are being used, which gives a side-cut brick, and an End Cut vs. 
active discussion is now going on as to the relative merits of 
the resulting brick. The side-cut brick is the more shapely 
and decidedly preferable for a building brick and for repress- 
ing, but as to which will make the more solid brick — the brick 
with fewer laminations— will have to be settled for each indi- 
vidual clay,* as the writer has seen cases where each has been 
decidedly preferable to the other.** The weak point of the stiff 
mud process is the laminations that must inevitably result from 
pushing a stream of clay through a fixed die. For the friction of 
the sides of the die will cause differential speeds in the flow of 
the clay, and these variations in the speed of the outflowing clay 
must necessarily result in laminations, or lines of demarkation 
between the different speeds in the clay bar, similar to the 
veins of a glacier. If the air has been expelled from the clay 
by the pug mill, these lines can be largely closed up again by 
a properly shaped die, as occurs in the glacier, and a first-class 
brick will result, in which the laminations will be inconspicuous 
and of no importance. But if the air has not been expelled, or 



*To one not experienced in working clays it may seem odd 
why a machine that is a success with one clay is a f ailure with 
others; but no two clays are alike, and the- individuality is 
often so marked as to require wide ranges in the methods of 
working different clays. 

**Tests recently made on several Ohio clays by Prof. Orton, 
Jr., seem to show that the side-cut are better than the end-cut; 
but the data does not admit of reliable comparison, except in 
one case, where the test was not satisfactory. ("The Clay- 
Worker," July, 1895.) 



30 VITRIFIED PAVING BRICK. 

the former and die are not properly designed, there will be an 
excessive amount of concentric lines that almost divide a cross- 
section of the brick into a series of shells or concentric cylin- 
ders, that greatly weaken the brick for withstanding blows or 
frost. The condition and character of the clay also greatly in- 
fluence these laminations, as the softer it is tempered or the 
more plastic it is, the more serious is this trouble. Hence the 
clay should be worked as stiff as possible, to not only make it 
dense and reduce the shrinkage, but also to reduce the lam- 
inations. A very stiff clay needs more power to work it, how- 
ever, and if too stiff, is very apt to break down the machine— 
the latter being a serious remedial fault of most auger machines. 
REPRESSING. — The most recent feature in pavers, which 
characterizes this season, is the sudden popularity of repressed 
brick, which are now being largely given the preference, at a 
considerable advance in price, to unrepressed brick. While not 
a new thing, the extra cost and the lack of indorsement by 
the brickmakers have held this more shapely brick in check 
in the past. Repressing consists in putting the freshly-made 
stiff mud brick into a die box and momentarily subjecting it 
to a heavy vertical pressure, which is usually applied on the 
fiat side.* This fills out the angles and edges, making a much 
more shapely, uniform brick, which is very slightly denser; it 
probably also decreases the laminations. There is no doubt as 
to the superior merits of a repressed brick as regards appear- 
ance and uniformity in size, but brickmakers are not satisfied 
as to the internal structure being benefited by breaking the 
old bond formed in the die by the very differently applied 

*This is done by a special machine known as the repress. 



VITRIFIED PAVING BRICK. 31 

vertical pressure. Nor are the tests altogether satisfactory that 
have thus far been made, which seem to indicate a somewhat 
smaller abrasion loss in the rattler, as this is largely, if not 
entirely, due to the heavy rounding of the corners in repressed 
brick, as against the square or slightly rounded corners of the 
unrepressed. For the tendency is to round the corners more 
and more, which gives a better footing to the horse and makes 
the brick more durable, and this year's brick are being rounded 
with a three-eighths-inch radius, where formerly only two- 
eighths to one-eighth was used. 

DRYING.— The stiff mud brick are hacked or piled in 
open checker work on cars as high as they will bear their 
own weight, or six to eight courses high, and dried in long 
tunnels or drying chambers, that are heated by direct fires, 
or steam pipes, or hot air. On account of the marked differ- 
ence in the drying properties of clays, the selection and de- 
sign of a dryer is a very important matter, and the dryer 
must be adapted for the specific clay. Some clays can be 
rapidly dried in eighteen to thirty hours without checking 
or injury, while others need forty-eight to sixty hours or 
longer, to avoid cracking to pieces. This means a great dif- 
ference in the size, arrangement and expense of operating 
the drying plant, which too frequently is neither appreciated 
by the brickmaker or the enthusiastic venders of patented 
dryers, and generally results in an insufficient drying depart- 
ment. 

BURNING.— We have now arrived at the most critical part 
of the paving brick business and the department that is mainly 



32 VITRIFIED PAYING BRICK. 

the cause of all the bad brick streets, and this is the more la- 
mentable as it is entirely in the control of the competent 
brickmaker if he has sufficient kilns, will personally super- 
vise this final department, and has the business sense, if 
not the integrity, to prevent underburned, brittle and checked 
brick from being sent out as No. 1 pavers. While first-class 
kiln burners, on whom must really depend the success in burn- 
ing, are none too plentiful, the fruit of their work is easily 
gauged by the watchful superintendent, who by conscien- 
tious classifying into four grades, can insure the delivery of 
50 to 80 per cent, of strictly first-class pavers. A serious 
fault with almost every paving brick plant in this country 
is an insufficiency of kilns, as they are the most expensive 
part of the plant, and yards that are otherwise equipped with 
complete outfits, including the very best and latest types 
of machinery, are frequently deficient in kilns, on which 
pre-eminently depends the quality of the brick. 

The kind of kiln employed for burning paving brick is 
Do wn= Draft 

Kilns. tne down-draft, whether round or oblong*, as the up-draft 

type produces too heavy a percentage of soft and overburned 

brick. A few brickmakers, who tenaciously cling to the ideas 

they learned when making building brick, try to burn pavers 

in clamp or other open top kilns, and succeed in making a 

few No. 1 or strictly hard pavers, and many No. 2 or soft 



*The round kiln, with a capacity of 40,000 to 80,000 brick, 
is the great favorite in Ohio, the leading State in the clay in- 
dustry, but the newer, less conservative western plants have 
mainly adopted the more convenient, large, rectangular kilns, 
which hold from 100.000 to 300,000 brick. 



VITRIFIED PAVING BRICK. 33 

pavers, and then try to find a customer who cannot distin- 
guish the inferior article. 

The continuous kiln has also been tried on pavers, but Continuous 

Kilns. 

has a discouraging field on account of the enormous shrink- 
age that complicates the maintenance of the feeding ports. 
Some recent improvements made at Streator and Galesburg, 111., 
in this type of kiln indicate that its well-known economy in 
fuel may yet be utilized for burning paving brick, with a 
reasonable yield of No. 1 brick. 

In burning the brick, which takes from seven to ten days, 
they are finally brought up to cherry or bright cherry heat, 
or from 1,500 to 2,000 degrees F., which is sufficient to vitrify 
most shales, but the impure fire clays require a higher tem- 
perature, or from 1,800 to 2,300 degrees F.* If shale brick 
are heated too hot, they soften and "wilt down," or melt into 
a more or less solid mass, yet it is usually necessary to bring 
them up to a heat which would cause them to stick together 
if not prevented by sand that is freely sprinkled between 
them in setting. At this temperature, when they border on 
the condition of a very viscous fluid, the lower brick be- 
come "kiln marked" by the weight of the upper brick forc- 
ing the lower brick slightly into one another, and care is 



*The writer is well aware that most clayworkers estimate 
their temperatures very much higher than given above, but 
many careful determinations with a reliable pyrometer (Le 
Chatelier's) have shown that paving brick clays almost in- 
variably vitrify within the above ranges of temperature. 
The clayworkers are still painfully misled by the very in- 
accurate determinations of the early, crude and erroneous 
pyrometers. 



Annealing. 



34 VITRIFIED PAVING BRICK. 

required to not allow this pressure to become too great by 
not setting them too high. Hence paving brick are set only 
twenty-two to thirty-four courses high, according to the ease 
of fusibility of the clay, whereas building brick are set thir- 
ty-five to forty-five courses high. Coal is used throughout in 
burning pavers, which do not need the preliminary or water- 
smoking stage to be done with wood or coke, as in burning 
building brick. Oil and natural gas have been used, instead 
of coal, in a few places that are so fortunate as to have these 
superior fuels within their command. They are far superior 
to coal in greatly reducing the labor in burning, and in pro- 
ducing a superior quality of brick from the uniformity of the 
fire, and the avoidance of the air checks that result from chill- 
ing, when cleaning the grate bars. 

After the kiln has beeD maintained long enough at a vitrify- 
ing temperature to heat the bricks through to the center, the 
kiln is (or should be) tightly closed,* and allowed to cool very 
slowly. Slow cooling is the secret of toughness, and the 
slower the cooling the tougher the brick. This annealing 
stage is grossly curtailed at most plants from insufficient 
kiln capacity, and the kiln is therefore hurriedly cooled down 
in three to five days, in order to hurry out the brick, even 



*Prof. Orton, Jr., has lately advised opening the fire doors 
and chimney flues while the brick are very hot, to hasten the 
cooling until the top brick reach a dark red, before closing up 
tight. This is a safe thing to do in the hands of an intelligent 
burner, as no harm will result if the air is raised to nearly the 
same temperature as the brick by entering the hot fire boxes 
and bags; but unless carefully watched, this is a dangerous 
risk to take. ("The Clay- Worker," April, 1895.) 



VITRIFIED PAVING BRICK. 



35 



to removing bricks that are so hot as to set fire to the trucks. 
At least seven to ten days should be allowed for cooling to 
secure a tough brick, and those who desire the best article 
can well afford to pay the extra cost of still slower cooling, 
if quality is the first consideration. 

If the kiln is properly burned, it will be found to have 
from one to four courses of top brick that are burned ex- 
tremely hard, but which are more or less air checked by 
being struck by the cold air in coaling or cleaning the fires. 
The top course is also more or less freely covered with an 
adhering film of ashes and dust, that have been carried over 
by the draft. Such bricks make excellent sewer or founda- 
tion brick, as they have a maximum hardness, crushing 
strength, and a minimum porosity. 

Beneath this top layer of checked brick, to within two 
to twelve courses of the bottom, are No. 1 pavers, or the 
brick that should be perfectly sound, completely vitrified, 
and have a maximum strength, hardness and toughness. Be- 
neath the No. 1 pavers are two to ten courses of brick which 
have not received sufficient heat to completely vitrify them, 
and are classed as No. 2 pavers, and used for the foundation 
or the flat course in paving. Beneath the No. 2 pavers are 
from one to six courses of brick which have not received 
heat enough to be able to withstand the frost, and are called 
"builders," as they are about equivalent in strength, hard- 
ness and porosity to hard burned building brick. 

With a fire clay, it is possible to produce 90 per cent, of 
No. 1 pavers, as there is no risk from overfiring, though 80 



Sorting. 



Field of 

No. i Pavers. 



36 VITRIFIED PAVING BRICK. 

per cent, is a high average. With shale, one sees frequent 
claims by patent kiln venders of 90 per cent, of No. 1 pavers, 
but such a very high percentage is rarely attained, with care- 
ful grading, while 80 per cent, is a high yield, or much above 
the average, and most yards do not get as high as 70 per 
cent, of strictly first-class or No. 1 pavers. 

PHYSICAL QUALITIES OP PAVING BRICK. 

COLOR. — The color of paving brick is no criterion for 
comparing brick made from different clays, as clays vary so 
greatly in kind and degree of color. Usually the impure tire 
clays give different shades of buff, while the shales give 
reds and browns. For a given clay the color is a reliable 
guide as to the heat a clay has received if it is burned under 
the same conditions, and the higher the heat, the darker a 
clay will be; but if the mode of firing the kiln is changed, 
as from an oxidizing to a reducing action, the clay will be 
made dark in consequence of this reducing action on 'he 
iron, and not by the heat; or a change in the fuel, as from 
Uniformity. °il or S as to coal, will usually result in a change in the color 
at the usual heat for this same reason. Uniformity of color 
on breaking the brick is a valuable guide in checking the 
work of the burner, as a black center in a red brick shows 
faulty firing, while a light colored center shows insufficient 
time in holding the heat. The outside color of the brick is 
often compromised and made valueless as a guide by the 
sand that is employed to prevent sticking in the kiln, or by 
fire flashing when using coal that is high in sulphur. 



VITRIFIED PAVING BRICK. 



37 



Some of the Ohio valley manufacturers resort to the trick 
of salt glazing the brick, which gives a dark gloss to the 
outside that is very attractive to the superficial observer, 
but totally defeats using the color test unless the brick is 
broken. This salt glazing has been the cause of many soft 
brick escaping the inspector's eye, and poor pavements have 
resulted, but the practice is fortunately becoming obsolete, 
as the glazing is only skin deep and soon wears oif, while 
inspection at the kiln can prevent the palming off of under- 
burned brick. 

STRUCTURE.— The structure of the brick, as regards its 
vitrification and homogeneity, are determined by the frac- 
ture on breaking the brick, as it is impossible to determine 
these vital questions from an exterior inspection. The vitri- 
fication should be thorough to the center, and free from large 
spots of unfused matter, which indicate sand 55 (quartz) or 
lire clay*; or very glassy or spongy spots, which show im- 
perfect crushing and mixing of a more fusible mineral in 
the clay. The structure should be uniform, devoid of air 
checks, and free from shakes or marked laminations, espe- 
cially if they are accompanied by air pockets. The edges 
should be free from "ragging," or serrations, arising from 
obstructions in the die, and the "kiln marks" or impressions 
from the overlying brick in burning should not exceed one- 
lift h inch in depth. The shape should be reasonably perfect 



*These sand spots are usually due to mixing surface clays 
with the shale or from imperfect stripping, while live clay 
seams sometimes occur in the shales. 



Salt Glazing. 



Homogeneity. 



38 



VITRIFIED PAVING BRICK. 



Variations 
in Size. 



Testing. 



and free from marked warping or distortion. Slight varia- 
tions in the size of the brick may be due to the wear of 
the die, variations in the shrinkage if the clay is not uni- 
form or hard burned, or to irregularities in the cutting table, 
if in length. The latter is of no importance, and if the for- 
mer are moderate they are of no consequence unless due to 
underburning, which is quickly discovered on breaking. If 
these variations do not interfere with the close laying of the 
brick, and the quality is otherwise satisfactory, they can be 
overlooked; but snug, close laying is essential to insure the 
durability of the pavement, and any warping or variation 
that prevents this should cause the rejection of the brick. 

HARDNESS.— The hardness of a paver is the property 
which enables it to successfully withstand the wear of the 
wagon tire, especially when the brake is applied, and the 
slipping of the horses' hoofs. Next to toughness or freedom 
from chipping, it is the most important requisite of a good 
paving brick. Though its great importance is recognized by 
engineers, and the inspector is ever alert for soft brick, yet 
an actual determination is rarely made, and then by the very 
imperfect grinding test, which is mainly a question of tough- 
ness rather than hardness or interpenetration. An indirect 
estimate of it is obtained by the absorption test, as a well 
vitrified brick is bound to be very hard, and hence a very 
low absorption standard will insure hard brick. But it is 
too important a matter to be arrived at indirectly, especially 
as very hard, excellent brick are found with 3 to 5 per cent, 
absorptions, and the writer suggests the use of Moh's scale 



a Frost Test. 



VITRIFIED PAVING BRICK. 39 

of hardness as a simple, quick, inexpensive way of arriving 
at the hardness. 

POROSITY.— The porosity of a paver is an excellent index 
of the degree of vitrification, as if sound and perfectly vitri- 
fied, it is almost non-porous. This porosity is measured by 
the amount of water the brick will absorb when soaked in 
water for 24 hours. The porosity is misapplied by many Misapplied as 
engineers as a critical index of the ability of the brick to 
withstand the action of frost, and amusing arbitrary lines 
are drawn, usually at 2 per cent , as to the maximum porosity 
that is permissible, often requiring less than many well- 
known building stones. This idea would be well founded 
if non-vitrified brick were used, which are not only 
very porous, but so lacking in strength as to be unable to 
withstand the disintegrating action of frost. As all paving 
brick are porous, to at least a degree, it is a question whether 
the disrupting action of the freezing water exceeds the 
strength of the brick; if the resistance of the brick exceeds 
the rupturing action of the crystallizing water, the latter 
will do the yielding, if it freezes, and it is immaterial how 
porous it is. Now vitrified brick, 'whether only incipiently 
vitrified, as in the impure fire clays, or completely, as in the 
shales, has a strength that greatly exceeds the disrupting 
action of frost, as shown by experience and tests*; hence, if 
the brick is vitrified and has the strength that usually ac- 

*Mr. A. D. Thompson, the city engineer of Peoria, 111., 
has recently made a very interesting series of freezing tests 
on hard and soft pavers, which show no effect whatever 
on hard brick, though disintegrating the soft brick. 



40 



VITRIFIED PAVING BRICK. 



Usual 
Absorption. 



companies vitrification, there is no fear of frost disintegra- 
tion, and this test should be used for its more restricted but 
still high value, as an expression of the degree of vitrifica- 
tion. So while the generally accepted rule that the less the 
absorption the better the brick . is true, up to a certain limit 
(or about 0.5 per cent ), a brick should not be condemned 
which otherwise gives satisfactory tests, especially if in the 
rattler, as is now done by many engineers, because it ab- 
sorbs 2 per cent or more of moisture. Most of the impure 
fire clay pavers rarely absorb as little as 2.5 per cent , and 
often over 5 per cent , yet they have been in successful use 
for upwards of twelve years without being affected by frost. 
Th oldest paving brick in this country, at Charleston, W. Va.,. 
which are still in fair condition after twenty-two years* 
service, absorb 4.5 per cent of water in twenty-four hours,, 
and are only hard-burned building brick, and made from a 
common though excellent clay. The Bloomington, 111., brick, 
that are being renewed this year (1895), after twenty years' 
service on their principal street, absorb 4.33 per cent , yet 
they show no signs whatever of frost action, though they 
have lost from one to one and a half inches from the top 
surface by wear, and are very rough, hand-made, "slop," or 
soft mud, building brick, made from a very poor, highly 
calcareous, glacial clay. The Sattler brick, a hand-made, 
fire clay 9x4x5 block, absorbs 5.5 per cent , yet they success- 
fully withstood the heaviest traffic of St. Louis, at the en- 
trance of the Missouri Pacific railroad freight yard, for seven 
years. 



VITRIFIED PAVING BRICK. 41 

The No. 1 shale pavers usually show less than 2 per cent 
absorption, and if carefully made, less than 1 per cent ; yet 
some of these almost non-absorbent shale brick are inferior 
in toughness and durability to the more porous fire clay 
pavers. An absorption of less than 0.5 per cent is apt to 
indicate brittleness, unless unusual care is taken in the an- 
nealing, and the best shale pavers range from 0.75 to 1.5. 

DENSITY.— Density is a desirable factor in paving brick, 
as, other things being equal, the denser the better, from the 
greater quantity of wearing material in a given space. The 
density is obtained by taking the specific gravity, or else 
the weight of a given size or a thousand. As different 
makers vary in the size of their bricks, it is dangerous to 
arrive at the relative densities by comparing the weights of 
a thousand brick, unless they are known to be of the same 
size; usually standard size unrepressed brick weigh about 
6,000 and repressed about 7,000 pounds per thousand. The 
specific gravity of a brick usually approximates that of the 
clay from which it is made, as the reduction in size from 
shrinkage is about offset by the loss in combined water. 
The shales range from 2.15 to 2.55 and average about 2.38 ^ ensit y of 
in specific gravity. The Coal Measure fire clays, whether 
pure or impure, range from 2.20 to 2.55 and average about 
2.40; the Mesozoic, or more recent fire and potters' clays, 
are lighter and range from 1.90 to 1.22 in specific gravity. 
The shale brick range from 2.05 to 2.55, and generally vary 
from 2.20 to 2.40. The impure fire clay brick, not having had 
the fire shrinkage completed, are usually lighter, or range 



Clays. 



42 VITRIFIED PAVING BRICK. 

from 1.95 to 2.30, and generally vary from 2.10 to 2.25. 

While a given clay will vary in density according to the 
amount of burning and the consequent shrinkage, this poros- 
ity, in consequence of not completing the shrinkage, must 
not be confused with the specific gravity, as the latter is 
primarily the individual weight of the molecules, and if two 
clays have been equally burned, the density will be the rela- 
tive weights of their molecules. If, however, the density 
has been unequally modified by difference in burning, then 
the porosity, as measured by the absorption, will have to 
be considered in arriving at an accurate idea of the density, 
though this can be ignored in vitrified brick as being too 
small for practical consideration. 

CRUSHING STRENGTH.— This property is very interest- 
ing as a matter of general information, especially as it shows 
that well vitrified brick sustain the greatest pressure known, 
outside of the metals;* but as a factor in the use of brick for 
paving it is not of much importance, as the poorest specimens 
Slight Value greatly exceed the heaviest load that ever comes upon them, for 
vitrified brick never fail by crushing, and Professor Baker re- 
gards this test as worthless.** It is a test that is usually 
required by the engineer, however, but more as a matter of 
custom than intelligent consideration, as the time would be 
more profitably expended in more thorough and elaborate 



as a Guide. 



* Tests at St. Louis, Cincinnati, Boston, Washington, Buda- 
Pesth, Berlin and other places have repeatedly shown the 
crushing strength of vitrified brick to be much greater than 
granite. 

**"Brick Pavements."— p. 8. 



VITRIFIED PAYING BRICK. 43 

tests of toughness and hardness, which are the desiderata 
for paving purposes. The highest crushing strength is given 
by the overburned brick, which are almost always too brittle 
to wear well, and hence mislead if guided by this test only. 
Paving brick vary greatly in crushing resistance, though the 
very wide differences that one sees in print are more usually 
due to the difference in the mode of testing or to the selec- 
tion of the samples.* Reliable samples show ranges as great Range in 
as 4,000 to 30,000 pounds to the square inch, and the extreme Strength. 
variations are found in the shale brick, which are conspicu- 
ous as being the best and the worst kinds of pavers, accord- ' 
ing to the clay, in other tests also; they usually range from 
10,000 to 20,000. The impure fire clay pavers show less varia- 
tion, or range from 6,000 to 14,000, and usually from 8,000 
to 12,000 pounds to the square inch. 

CROSS-BREAKING STRENGTH.— This test, which is also 
known as the modulus of rupture, is of greater value than 
the crushing test in discussing paving brick, as the methods 
of testing differ but slightly, and it is conceivable that this 
determination may be of direct value where the brick have 
a very poor foundation. Still as brick are actually laid and 
used, they rarely break unless worn out, and like the crush- 
ing test, too high a value is given to it by engineers. It is 
preferable to the crushing test as a guide, as it introduces 
the question of tensile strength, which is an important func- 

*Some tests to be found in the current press are self-evi-: 
dent cases of juggling, as they have undoubtedly been se- 
lected from the worst samples of rival brickmakers, a too 
common method of carrying on commercial warfare. 



44 VITRIFIED PAVING BRICK. 

tion of the toughness. The cross-breaking strength ranges 
from 1,000 to 3,300, and usually amounts to 2,000 to 3,000 
pounds per square inch of cross section, as tested between 
supports set six inches apart and loaded in the middle. 

TOUGHNESS,— This is the crucial test of a paving brick, 
and greatly exceeds in importance all the other tests com- 
bined. This is pre-eminently the test that will show whether 
a brick will prove satisfactory in practice, and which of two 
or more samples will be the more enduring. For this test 
directly recognizes the severe factor that chips and shatters 
the brick, or the blows of the calks of the horses' hoofs, 
and the bump and abrasion of the wagon tire. It is the near- 
est approach, concentrated in a few minutes, of the treatment 
that a brick receives from traffic. If this test is satisfac- 
tory, no fear need be felt as to the results in practice, no 
matter how unsatisfactory the other tests may be. Although 
this test is always made with a foundry rattler, unfortu- 
nately no two engineers conduct the test alike, so that re- 
sults by different parties are very dangerous to compare, and 
until some uniform method of conducting this test is adopted, 
The Rattler. it is sa f er no ^ ^o make comparisons of different authorities. 
The test is made by putting several brick in a rattler, or re- 
volving iron barrel, with more or less scrap iron, and some- 
times with so-called standard pieces of granite. The rattler 
is then revolved at speeds that vary with each engineer, and 
for variable times. The result of the impact and abrasion 
of the brick and iron on each other is to rapidly wear off 
the angles and edges, and to knock off chips, if brittle; and 



VITRIFIED PAVING BRICK. 45 

this loss, expressed in percentages of the original weight, 
gives the rattler loss, which is the best guide yet obtained 
to determine the wearing quality of a brick. While this is 
the general method of carrying out this test, the results will 
greatly vary with the size, speed and time in the rattler; 
with the amount, kind and number of pieces of scrap iron 
and granite employed; whether hung on trunnions or a shaft; 
with the size, dryness and number of brick in the test, and 
with the character of the lining of the rattler. Thus Prof. 
Baker has shown that granites vary as much as 600 per cent 
in the loss sustained in the rattler, while different kinds of 
scrap iron and steel are liable to vary still more in their rel- 
ative loss and therefore abrasive action on the brick. This 
confusion is so great, and leads to such variation in the re- 
sults, that at last a committee has been formed by the Na- 
tional Brickmakers' Asssociation to adopt a standard method Usual Loss. 
of carrying out this very important test. As tentative re- 
sults, it may be mentioned that vitrified brick show a loss 
of 1.6 to 35 per cent , usually from 5 to 15 per cent , while 
granite, under similar circumstances, suffers a loss of 2 to 
13 per cent , and usually from 3 to 5 per cent. It is worthy 
of notice that in a few instances, where granite and brick 
were tested side by side, some of the brick were tougher 
than the granite, which speaks volumes for the future, and 
shows that, with more care in manufacture, this excellent 
pavement can be safely used for the severest traffic. In 
tests made in Boston*, on eighteen different samples of pav- 



"Engineering News," June 2, 1892. 



Influence of 
the Corners. 



46 VITRIFIED PAVING BRICK. 

ing brick with granite in the same rattler, five of the brick 
showed a smaller loss than the granite. Tests made at Cor- 
nell University** on twenty-five samples, representing seven- 
teen different makers of brick, with trap (a tougher rock than 
granite) as the standard of comparison or 1.00, a shale 
brick showed a loss of only 0.87, and a thoroughly vitrified 
fire clay brick showed a loss of only 1.66, while the others 
ranged from 3,31 to 17.18, and averaged 8.3. 

When square-cornered brick are tested with those with 
rounded corners, the former show a much greater loss, as the 
sharp angles break off readily. This, however, is just what 
happens in practice, and is a fair comparison as regards brick 
to brick, but is unfair as a test of the clays, as they should 
have similar corners to give a reliable comparison. Prof. 
Baker's tests show that square-cornered brick lose about as 
much in the first half hour as in the subsequent hour, and 
he advocates rattling the brick for an hour, before the test, 
to wear off the edges and angles; this is very objectionable, 
as brick are expected to hold their edges and angles in serv- 
ice, and not wear to a cobblestone; and if they are not tough 
enough to do this, the rattler test should be so conducted as 
to bring out this information. 

METHOD OF TESTING PAVING BRICK. 

EYE EXAMINATION.— There is no more satisfactory meth- 
od of arriving at the merits of a paving brick than by the 
trained, experienced eye, when assisted by the free use of a 



** "Engineering News," April 18, 1895. 



Tests. 



VITRIFIED PAVING BRICK. 47 

hand hammer. A critical examination by the eye and hand 
hammer, combined with proper experience, can usually detect 
the pros and cons of a brick as well as an elaborate series 
of tests, and in a few minutes while the laboratory tests take 
hours. But unfortunately the English vocabulary is too lim- 
ited to make the nice distinctions that is possible to the trained 
eye, and it admits of no satisfactory standards if a numer- Necessity of 
ical evaluation is attempted. As in most expert work, it is a 
personal decision that is founded on good judgment, training, 
and experience that cannot be transferred, and while it leaves 
little to be desired when backed by integrity for the numerous 
and rapid decisions of municipal engineering, it is testimony 
that can be besmirched and impugned when attacked by un- 
principled self-interests, unless sustained by a cyclopean repu- 
tation. As it is only the limited few whose reputation can 
overwhelm malignant inuendoes, and as specific figures are 
required for general use, a series of tests have been devised 
which admit of general application and enable definite stand- 
ards to be attained and lived up to. The necessity of such 
definite figures is so well recognized that there are not only 
numerous testing laboratories scattered all over the country, 
but city engineering department laboratories are being or- 
ganized to frequently and rapidly furnish specific information 
when differences of opinion arise between the contractor and 
inspector about the quality of brick. At present the inspec- 
tion of the brick is carried on at the work in the street, 
when about to be laid, and the condemned brick are a serious 
expense to the contractor, who is often an innocent sufferer, 



should be at 
the Kiln. 



48 VITRIFIED PAVING BRICK. 

and are a menace to the vigilance of the inspector, as they 
have a curious way of disappearing around the corner and 
Inspection reappearing laid in the street. The proper place to inspect 
the brick is at the kiln, where it can be much more rapidly, 
easily and safely made, and where there is no such strong 
incentive to smuggle condemned brick into the work. For 
even if the work is done under a maintenance bond, the con- 
tractor is usually willing to take risks as to the durability of 
questionable brick that the cautious engineer would not en- 
tertain. 

LABORATORY TESTS.— The tests that are usually relied 
on to determine the merits of a paving brick are: 

I. Density, or specific gravity. 

II. Absorption, or porosity. 
-III. Crushing strength. 

IV. Cross-breaking strength. 

V. Hardness. 

VI. Rattler test. 

The determination of the crushing and cross-breaking 
strengths requires a large testing machine of at least 150,000 
pounds capacity, which is expensive and usually to be found 
in only well-equipped testing laboratories. But every city 
and brick plant should have a balance ($5 to $35), hardness 
scale (50c), and rattler ($25 to $80), with which to make the 
other tests, which are the most important, and only require 
a moderate outlay if power is available for running the rattler. 

DENSITY.— The density or specific gravity test is made on 
half brick or chips after they have been soaked in water for 



VITRIFIED PAVING BRICK, 49 

twenty-four hours to fill the air spaces. A whole brick should 
not be used, as the water cannot usually penetrate into the 
voids in twenty-four hours when the skin surface is sound 
and the brick is vitrified. It is preferable to take only a 
small fragment and weigh accurately on a chemist's* balance 
to 1 in 10,000, rather than attempt to obtain it by using a half 
brick and a druggist's scales, as usually employed, which only 
weigh to about 1 in 300. The density is calculated by the 
formula : 

W 



in which D = the specific gravity in terms of water. 

W = weight in air before soaking. 
' W — " " " after 
W" — " " water after " 

ABSORPTION TEST.— The absorption test, to determine the 
relative porosity of a brick, which is so valuable as indicating 
the degree of vitrification, is made in several different ways, 
and published results are by no means concordant in conse- 
quence. It is obtained by immersing the brick in water for 
more or less time, and determining the increase in weight 
resulting therefrom. The brick is not always dried before 
immersion, nor always wiped dry thereafter, while the length Variations in 
of time in water varies from half to seven days. Some take lasting. 
a whole brick and others only half a brick, which latter 
introduces the independent questions of laminations and air 



*Excellent balances for this purpose are sold by the chem 
ical dealers for $15 to $35. 



50 - VITBIFIED PAVING BRICK. 

spaces. The latter are very important matters, but their 
effect is better shown in the crushing and breaking tests, 
and as this is solely to show the porosity, this test should be 
made on a sound, whole brick, unless a chip is taken as sug- 
gested below. While the length of exposure is arbitrary, ex- 
periment shows that twenty-four hours is necessary to approxi- 
Hour lately fill up the pores, after which the brick very slowly in- 
Standard, creases in weight for weeks. As such a long time is prohibitory 
and unnecessary, I would suggest that twenty-four hours be ac- 
cepted as the standard time for soaking, previous to which 
the brick should be thoroughly dried at 212 degrees F. or 
higher (unless taken fresh from the kiln), and that after the 
twenty -four hours' exposure in water they be wiped perfectly 
dry with a towel before weighing. The difference between 
the weights before and after immersion, divided by the 
former, gives the percentage of absorption or porosity, ex- 
pressed in its own weight, or: 

W v -W 



w 

in which W — weight before immersion. 

W v — " after " 

P = porosity. 

While it is the custom to take a whole brick for this test 
and use a druggist's balance, it is much quicker and more 
accurate to take small, sound chips, which can be thoroughly 
dried in a few hours, and weigh with a chemist's balance. 
This is far more reliable, satisfactory and quicker, as it is 
never certain when a large brick is thoroughly dried out, 



VITRIFIED PAVING BRICK. 



51 



unless exposed at a heat above 212 degrees F. for several days. 

If the brick are salt glazed, a practice that is still carried 
on to some extent in Ohio, a chip should always be taken, as 
such brick are practically impervious to water if the skin is 
unbroken. But as the glazed surface soon wears off in service, 
when the water gets access to the interior, the brick should 
be tested so as to give the porosity of the body of the brick, 
as that is what will have to stand the wear. Hence a frag- 
ment should be used, for this test, which eliminates the 
short-lived skin surface. 

To show that the absorption test gives only relative values, 
and never absolute, and to emphasize the importance of adopt- 
ing a standard period for soaking the brick, the following 
tests are given, which clearly show the absurdity of trying to 
saturate a brick in a 24, 48 or 188 hours' test. 

These tests are selected from a series made on chips from 
brick representing all kinds of clays, and show a much more 
rapid rate of, absorption than would have been exhibited by 
whole brick. For the thinner the chip, the more rapid was 
found to be rate of absorption (or drying), as would naturally 
be expected, but with the size of chips used, or from one- 
fourth to one inch in thickness, this did not show materially 
until after one day's soaking. If these chips, with an average 
thickness of half an inch, required over eight weeks to saturate 
them, the time required for the water to entirely penetrate a 
brick from five to six times as thick must be very much longer. 

The saturated samples were allowed to air-dry in a room 
protected from wind and sun, with a temperature ranging from 



Salt Glazing. 



Tests of 
Absorption. 



52 



VITRIFIED PAVING BRICK, 



SO to 90 degrees F., and found to lose their water at the rates 
shown in the table. The speed of drying will be largely a 
question of the dryness and temperature of the air, and hence 
will fluctuate greatly. They are added to show that brick 
slowly parts with its water, though more rapidly than it ab- 
sorbs water, which should be remembered in drying brick be- 
fore testing for absorption. This emphasizes the desirability 
of using fragments, and heating them over a heater, to quickly 
insure perfectly dry material on which to make the absorption 
test. 

SPEED OF ABSORPTION. 
Table Showing the Rates of Absorption of Paving Brick. 



Time. 



Ten hours 

Twenty hours.. 
Twenty -fo'r hs 
Thirty hours.. 

Three days 

Six days 

Twelve days. . 
Twenty days.. 
Thirty days — 

Forty days 

Fifty days 

Sixty days 



Common Clay. 



Charles 
ton. 



4.40 % 



4.90 
5.39 

5.58 
5.79 



Bloom - 
ington. 



4.33 fc 



4.83 
5.25 
5.41 
5.68 



Fireclay. 



Sattler. 



5.37 

5.48 



5.49 
5.54 
5.90 
6.16 
6.37 
6.60 
6.93 
7.15 
7.25 



Mack. 



3.35 % 



3.82 
4.24 
4.58 
4.73 



Pure 
shale. 



Stand 
ard. 



0.44 % 



0.75 
0.82 
0.96 
099 
1.03 



d>> 
© o 



St. Louis 



0.62 i 



1.03 
1.09 
1.16 
1.36 
1.37 



VITRIFIED PAVING BRICK. 



53 



RATES OF DRYING. 

Table Showing the Rates of Drying* Paving Brick. 





5.79 <f> 


5.68 <f 


7.25 $ 


4.73 <f 


1.03 <f 


1.37 <f 


Fifteen hours . 


1.75 


1.20 


1.73 


0.34 


0.40 


0.52 


Twenty- four hs 


1.43 


0,87 


1.32 


0.14 


0.38 


0.49 


Thirty hours. .. 


1.22 


0.66 


0.74 


0.05 


0.33 


42 


Forty eight hrs 


0.90 


0.38 


0.03 


0.00 


0.21 


0.37 


Six days — 


0.09 


0.00 


0.00 


0.00 


0.18 


0.18 


Ten days 


0.00 


0.00 


0.00 


0.00 


0.09 


0.09 



•Using the previous specimens, after being soaked to their respec- 
tive maximum amounts as given before. 

CRUSHING TEST.— The crushing resistance of brick is 
determined in such different ways as to give great variations 
in the reported values per square inch. They are- tested as 
cubes, flatways and edgeways, after being trued up with a 
bedding of plaster of paris, blotting paper, and by grinding. 
While the test is not necessary for use in paving, as the 
crushing strength so greatly exceeds the load ever put on 
it, it is valuable for comparison, provided the tests are made 
in a similar manner. For Prof. Ira Baker found that the 
strength of a brick tested endways, edgeways and flatways 
was as 2:3:4, while the difference between an approximate 
or yielding bed, as blotting paper, plaster, wood, etc., and 
true-ground parallel beds was found by Prof. J. B. Johnson* 
to be 25 to 100 per cent. The method adopted by the latter 
authority is the best thus far devised for giving the time 
strength of the brick, and is well worthy of universal adop- 
tion. In Johnson's method the edges are ground perfectly 



Variations in 
Testing. 



♦"Engineering News," April 18, 1895. 



54 VITRIFIED PAVING BRICK. 

true and parallel, securing the latter by grinding one side as 
a datum, on a stone-polishing table, and then crushing the 
brick edgewise, after carefully aligning in the machine, which 
gives a height that is about double the width of the column 
under test, and is the way in which the brick is used in 
practice. The results obtained by this method are much 
higher, in consequence of the trueness of the crushing faces, 
which, though somewhat expensive to make (the stoneyards 
charging $1 per brick for grinding the faces), gives results 
that can be reliably compared. 

CROSS - BREAKING STRENGTH. — The cross - breaking 
strength has been universally determined by supporting the 
brick between two steel knife edges set six inches apart, and 
applying the load in the center by another knife edge, all the 
edges being rounded. From this the modulus of rupture (R) 
is determined by: 

3W1 
R 



2 bh2 

in which W — breaking load in pounds. 
1 = length between supports, 
b = breadth of brick, 
h — height " 
R ==> modulus of rupture in pounds per square inch. 

Recently Prof. Johnson* has proposed to place the supports 
seven inches apart, instead of six, and to compare the break- 
ing load in terms of inch width, thus ignoring the size of the 
cross-section. His claims for this radical departure are that 

*Ibid. 



VITRIFIED PAVING BRICK. 



55 



the modulus of rupture is not UDderstood by practical men, 
nor does it do justice to deep brick. As this test is made 
by engineers for engineers, as brickmakers have a much 
quicker though inexpressible way of arriving at the merits 
of a brick by the trained eye and hammer, and as the stand- 
ard method is a specific determination of the rupturing value 
of a square inch of the brick, the writer sees no justification 
for departing from a conventional definite statement for an 
indefinite one. For the object of the tests is to primarily 
give the value of a certain clay as made up into a given 
brick, and as no two clays are alike, and as the same clay 
may give very different results, according to how it is 
manipulated in manufacturing, the tests should aim to ex- 
press solely the quality of the brick, and not also its quantity 
or size, which is what Prof. Johnson's method does. If the 
quality of clay is satisfactory but the size of a brick is not, 
the die and molds are easily changed, if the engineer prefers 
a deeper brick. 

HARDNESS.— The hardness has hitherto been rarely de- 
termined, and then by grinding the brick on a polishing 
table, and taking the amount ground off as a measure of the 
hardness. As this grinding action introduces the factor of 
toughness as well as hardness, it is a very unsatisfactory 
test, and is now seldom made. A simple, quick test that cor- 
rectly gives the hardness is Moh's scale of hardness, which 
is the principal tool of the mineralogist. In this scale, which 
runs from No. 1 or talc, which can be readily scratched by 
the finger-nail, to No. 10 or the diamond, the hardest sub- 



Objections to 

Johnson's 

flethod. 



Moh's Scale. 



56 



VITRIFIED PAVING BRICK. 



stance known, only Nos. 6 and 7 interest the tester of paving 
brick, as brick are too soft for pavers that are not as hard 
as 6, and most pavers are between 6.5 and 7.0. No. 6 is 
feldspar, or the white to pink mineral that constitutes about 
75 per cent of the granites, and No. 7 is quartz, the hardest 
of the common minerals, which is the colorless, glassy con- 
stituents of granites. In applying the tests, a sharp edge or 
angle should be tried on a smooth face of the object being 
tested, and a firm, strong pressure applied. Substances of 
equal hardness scratch each other with equal facility, while 
Mode of if there is a difference of 0.5, as, say, 6.0 and 6.5, the sub- 
Testing, stance that is 6.5 will be barely scratched by the 6.0, but it 
will readily scratch 6.0; a substance that is 7.0 in hardness 
is not affected by 6.0, while it very readily scratches 6.0. 
Practice is needed to make fine distinctions, lacking which 
the determination should not be attempted closer than 0.5, 
and the white dust that results from the scratching should be 
rubbed off before deciding which is the harder substance. 

RATTLER TEST— The abrasion or impact test, as the rat- 
tler test is also called, is decidedly the most valuable means of 
arriving at the durability and relative value of paving brick, 
but, as previously mentioned, nearly every engineer has a differ- 
ent way of carrying it out. As the rattler results are jointly de- 
pendent on the toughness, or the ability to stand shock, and 
the hardness, or the ability to withstand abrasion, it will 
depend on how the test is conducted as to which of these 
two factors is given the greater prominence. Now the hard- 
ness of a brick can be quickly and satisfactorily determined 



VITRIFIED PAVING BRICK. 57 

with pieces of quartz and very hard steel, and while the 
harder the brick the better, the most severe action on a 
paving brick in service, and what most quickly gets the 
pavement in bad condition if the brick are inferior (brittle or 
soft), is the blow of the horses' hoofs, especially of the toe- 
calks. Hence the rattler should be run to bring out this 
weakness, and as much, impact as possible secured in running 
it. The speed should therefore be such as to carry the brick 
high enough up the sides of the rattler as it revolves to let 
them fall back (impact), and not slide back (abrasion), and 
the diameter should be large enough to permit the brick to 
fall and tumble over one another, while the number being 
tested should not be so great as to interfere with this falling 
and tumbling action. If cast iron or granite are used, they 
should be large pieces, to get a blow; but here the writer Foreign 
fails to indorse present rattler practice, and would allow noth- 
ing to be put into the rattler with the brick to be tested ex- 
cept enough standard brick to fill out the complement, if only 
a few are to be tested. For the character of the foreign 
matter added, whether scrap iron or granite, has such a 
marked influence, according to its size, shape, angularity and 
hardness, and it is so difficult to maintain uniformity in the 
conditions, as the pieces are continually wearing lighter, 
rounder and less wearing in their action, while duplication 
is so difficult, that the writer would omit them entirely, in 
order to make reliable comparisons. The tumbling, rolling 
and sliding of the brick over each other will be more than 
ample to compensate for the loss of the foreign matter by 



flatter. 



58 



VITRIFIED PAVING BRICK. 



Standard 
Rattler. 



•♦Fillers." 



running the rattler a little longer. As this method will need 
further testing before a standard size, speed, time and num- 
ber of brick can be adopted, it is premature to specify such 
data; but experience suggests that the diameter be at least 
30 inches, with a length of at least 36 inches; that the shape 
be polygonal; that the number of brick not exceed 25 per 
cent, of the volume of the rattler; that the speed be between 
20 and 30 revolutions, and the test to continue for 1 to 2 
hours. The rattler should be hung on trunions, and not 
have a shaft run through it, which endangers brick jamming 
between the shaft and shell; it should be perfectly horizontal, 
with large spaces between the staves (say one inch) to permit 
the prompt escape of the chips. Rattlers have been made of 
wood, cast iron and steel. Wood has the advantage of not 
polishing and being more uniform, which are two objection- 
able features in cast iron; bars of mild steel would be more 
durable, and perhaps as satisfactory as the wood, especially 
in not giving so much variation in diameter from wear. A 
committee of the National Brickmakers' Association is now 
considering a standard system of tests, and the fruit of their 
labor is anxiously awaited. 

As there are liable to be times when only a few brick are 
to be tested, a stock of standard brick should be kept on hand 
of the best kind available, and the requisite number taken to 
fill out the full complement for a test. These standard brick 
could be selected by a maker with considerable confidence as 
to their uniformity, and if the trouble is taken to burn the 
last kiln of the season for this purpose, when the kiln can be 



VITRIFIED PAVING BRICK. 59 

shut perfectly tight and allowed to cool for weeks, a stock 
could be obtained of many thousand that could be sent all over 
the country. Such carefully made and selected brick are 
apt to be more uniform than granite or any natural stone, with 
their defects from quarrying, tooling, joints, decay, and lack 
of homogenity, and decidedely more so than iron or steel stand- 
ards, unless the latter conform to strict physical and chemical 
specifications. Such a method of conducting the rattler test 
would give harmonious results that could be duplicated at any 
time or place, and on which comparisons could be safely made. 
EVALUATION OF THE RESULTS.— The final deduction 
to be drawn from these different tests, and the weighing of 
their respective values, is a subject that is now under active 
discussion, and a standard rule or formula is urgently needed. 
The attempts thus far made are all open to serious objections, 
and it is still premature to settle on a final value for the co- 
efficients or factors until a standard method of making the 
tests is adopted; the writer therefore offers the subsequent 
formulae as a guide for framing such a standard, rather than 
for its intrinsic merit. 

One of the earliest authorities to discuss this matter was _ , 

Baker's 
Prof. Ira Baker, who, in a valuable pamphlet entitled "Brick Method 

Pavements," published* in 1891, puts an equal value on trans- 
verse-strength, absorption and rattler tests ; he regards the 
crushing test as worthless, while he erroneously confuses ab- 
sorption and density as both being represented by the porosity. 



*By the Clay-Worker, Indianapolis, Ind. 



St. Louis 
flethods. 



GO VITRIFIED PAVING BRICK. 

The Board of Public Improvements of St. Louis, through a 
special committee,* adopted formula I, while Prof. J. B. John- 
son** devised formula II for arriving at V, or the comparative 
value of paving brick: 

10 1 T' C 

V= + — -4- + ---I. 

R G 4 A 2000 4000 

T / C 

V = (25-R) + (3-A) + -f - - II. 

1000 4000 

in which V = an arbitrary comparative rating. 
R G = rattler loss in terms of granite. 

R == rattler loss in percentage of the weight of the brick. 
A = absorption in percent of the total " " " " „ 
T' = transverse strength per inch width. 
C = crushing strength per square inch. 

Both of these are based on tests made by Prof. Johnson for 
the city of St. Louis on samples that were sent by seven manu- 
facturers. 

In formula I each factor appears as a multiple (or divisor), 
and is therefore more sensitive to variations than II, in which 
only two so appear. The rattler loss is based on the very ob- 
jectionable granite rating in I, or a variable unit, while in 
both the transverse strength is rated in terms per inch width 
of the brick on a seven-inch span, while the modulus of rupture 
per inch of cross-section has been the universal and the more 
valuable unit, on a six-inch span. The hardness and density 
is also ignored in each, though the former is. the most vital 



* "Engineering News," July 26, 1894. 
** "Engineering News," April 18, 1895. 



VITRIFIED PAVING BRICK. 



61 



factor of durability, excepting toughness, and should certainly 
be considered. 

The writer therefore suggests the following to overcome 
these objections, and as only four factors have thus far been 
usually given, formula III is for such incomplete data, while 
formula IV is the proper one to use if all six factors are given: 

T C 

V— (18-R) 6 + (7-A) 4 + + HI. 



V = (18-R) 5 -f (7-A) 2 + 



220 
C 



1000 



T 

h- 

220 1000 



10 



10 



+ 



— + 



-IV. 



3.25-D 7.5-H 



in which V = as before. 

R= " 
A= " 
C= " 

T = Modulus of rupture per square inch. 
D = Specific gravity. 
H = Hardness by Moh's scale. 

To show the application of formula IV, and its great con- 
venience in comparing brick of nearly equal value, the follow- 
ing example is given, which is based on two shale brick of 
superior quality and much above the average (or 100): 







a 










Brick. 




o 

0. 


,d 

rH Si) 






CB 

GQ 

a 






o 


w 5 


m 


-a 




-tf GO 

d o 


DO 

< 


H02 




© 


M 




Percent. 


Per cent. 


Pounds. 


Pounds. 






Purington 


5.87 


1.12 


3,380 
2,460 


13,220 
15,460 


2.31 


6.75 


Standard 


4.95 


.55 


j 

2.41 


6.75 







Wheeler's 
Method. 



G2 VITRIFIED PAVING BRICK. 

When these values are substituted in IV the respective 
merits of the brick work out as follows: 

3380 13220 

Purington — (18-5.87) 5 + (7-1.12) 2 -\ 1 h 

220 1000 
10 10 

_j_ = 124-7 

3.25-2.31 7.5-6.75 

2460 15460 

Standard = (18-4.95) 5 + (7-0.55) 2 -4 1 1- 

220 1000 
10 10 

+ — 1 30. 1 

3.25-2.41 7.5-6.75 

Or their relative values are as 124.7 to 130.1. 

In arriving at the relative weightings of each factor, the 

following mean values of the St. Louis series of tests are used, 

as formulae I and II are based on them: 

R = 16.5 per cent. 
RG= 4.7 " " 
A= 1.25 " " 
T / = 3 300 pounds. 
C = 13.000 " 

In deducing mean values for III and IV a careful study was 
made of a large number of tests from all over the country, 
from which 262 were sifted out that seem to have been made 
with sufficient care on reliable samples as to be entitled to con- 
sideration, which gave the following: 

R = 8.0 per cent. 
A = 2.0 " " 
T = 2,200 pounds. 
C = 10.000 " 
D = 2.25 
H = 6.5 



VITRIFIED PAVING BRICK. 



63 



These average values will give a rating of 100 for an aver- 
age brick, if tested in the usual manner. 

— Comparison of the Weightings of the Factors.— 




In arriving at this weighting, the writer has placed a value 
on the rattler test equal to all the others combined, as this so 
nearly duplicates the impact and abrasion that the bricks re- 
ceive in the streets, only the severity of the test is so great 
that an hour's tumbling »in the rattler is equivalent to years of 
service in a pavement. If a brick satisfactorily meets this se- 



Importance of 
the Rattler 
Test. 



'Brick Pavements," the Clay- Worker, 1891. 



64 



VITRIFIED PAVING BRICK. 



Variations in 
Paving Brick. 



vere test no fear need be felt in using such a brick, no matter 
whether the evidence of the other tests is favorable or not. 
The other factors give evidence that is valuable, but none of 
them can be used alone or collectively, as the question of 
toughness is only satisfactorily shown in the rattler test. They 
are given equal value by the writer until more thorough tests 
have been made, except when only four factors are given, 
when a double value is put on the absorption, as this is then 
the only exponent of the hardness, density and porosity. 

UNIFORMITY OF RESULTS.— In testing brick at least 
five specimens of each lot or kind should be tested, and prefer- 
ably ten, and the results averaged for use in the formula. If 
the samples are taken from different kiln runs and made at 
different times, it adds greatly to their reliability if the indi- 
vidual tests closely agree; but if the results vary greatly, such 
a clay is open to suspicion until careful resampling and testing 
shows whether it is due to careless sorting or to manufacture. 
The best brick vary from 15 to 30 per cent, in the tests, while 
inferior brick exceed 50 per cent , and this range is a very 
valuable check on the care in making the brick, and on the 
sorting in loading. To illustrate the variations that usually 
occur in testing paving brick, the following table gives results 
obtained by Prof. Johnson on samples furnished by the manu- 
facturer to the city of St. Louis: 



PROF. JOHNSON'S TESTS FOR THE CITY OF ST. LOUIS. 

SUMMER 1894. 





X 

C 

2 


Cross-break 


Crushing 


Rattler. 


s 

(X 


h 

O 


Name op Brick. 


persq.inch. 


persq.inch. 


^2* 
o 

us 

EH 


Brick. 


Granite 

1 


o 

•a 

© © 


o ^ 




- m 

on-rj 

§1 


ED 

bog 
S-, O 


► OQ 

X 


oa 

bo3 

> 
< 


m-ta 

1> id 

v u 


© © 
OD© 

oS 

< 


4> © 

s ° 

© s- 

*" © 


© © 

be© 

> p* 

< 




00 rt 
®g 

is i- 

3.1 

to 

3.7 


© © 

tx © 
as 

© © 


*Mack Brick Co., 

New Cumberland, W. Va. 

Repressed Fire Clay. 


5 


2,259 

to 

3,707 


2,959 


10,200 

to 
over 
14,000 


12,000 


y 2 


12.00 

to 

21.40 


15.10 


2.6 

to 

4.8 


(20) 
3.6 


420 


3.40 


Purington, 

Galesburg, 111. 


5 
5 

5 


2,860 

to 

3,688 


3,112 


Not 

b'keu 


16,770 


y 2 


12.30 
to 

14.80 


14.30 


4.82 
to 
12.9 


do. 


400 


0.91 
to 
1.'60 


1.05 


Terra Cotta Co., 

Galesburg, 111. 


994 

to 

3,851 


2,646 


13,540 

to 
23,920 


18,730 


y 2 


11.20 

to 

31.60 


19.78 


do 


do. 


549 


0.36 
to 
1.16 


0.63 


Wabash Clay Co., 

Veedersburg, Ind. 


2,427 
to 

3,755 


3,097 


13,150 


12,490 


y 2 


7.99 
to 
13.61 


11.03 


do. 


do. 


307 


0.90 

to 

1.35 


1.12 


Alton Paving Brick Co., 

Alton, 111. 


5 


1,935 

to 

3,377 


2,690 


8,424 

to 

19,490 


(9) 
12,5f0 


y 2 


16.13 

to 

34.46 


(8) 
22.50 


do. 


do. 


653 


0.60 

to 

1.11 


0.88 


St. Louis Press Brick Co., 

Glen Carbou, 111 


5 
6 


1,855 

to 

3,112 


2,421 


12,300 

to 
over 
20,000 


13,190 


y 2 


12.57 
to 

32.00 


19.75 


do. 


do. 


549 


0.20 

to 

0.62 


0.33 


Moberly Brick Co., 

Moberly, Mo. 


2,586 

to 

3,314 


3,029 


9,730 
to 

18,440 


15,360 


y 2 


13.00 

to 

24.00 


16.30 


3.4 
to 

5.6 


(5) 
4.1 


400 


1.47 
to 

3.51 


2.80 


Gaffney Brick Co., 

Atchison, Kan 


5 


2,580 

to 

4,475 


3,185 


16,590 

to 
28,400 


20,183 


X A 




26.67 


4.82 

to 

12.9 


3.6 


741 


0.23 
to 

0.58 


0.55 


St. Joseph Press Brick Co., 

St. Joseph, Mo. 


6 


2,236 

to 

4,531 


3,214 


5,740 

to 

15,580 


11,255 


y± 


7.50 
to 
10.40 


8.70 


2.1 
to 
2.3 


2.2 


395 


0.89 
to 

1.88 


1.49 


New Philadelphia, 

Kansas. 


6 


1,233 
to 

2,864 


2,389 


9,900 

to 

18,330 


13,300 


y 2 


8.40 
to 
28.50 


15.30 


4.4 

to 

6.1 


(5) 
5.0 


310 


2.03 

to 

3.81 


2.92 


Ottumwa Press Brick Co., 

Otumwa, la. 


2 


1,678 

to 

2,430 


1,960 


7,435 

to 

9,820 


8,600 


y 2 


5.00 
to 
23.40 


14.50 


2.0 
to 

2.8 


(3) 
2.3 


420 


3.4 


3.40 



*Note.— These are all shale brick except the Mack, f Average of tests. 



66 



VITRIFIED PAVING BRICK. 



VALUE OF THE RATING FORMULA —The great value 
of a rating formula for deducing a specific comparative value 
of each brick (provided it is properly weighted and correctly 
designed) is well shown by the following example, which is 
based on tests made by Prof. Johnson for the city of St. Louis. 



TABLE SHOWING COMPARATIVE RAT 



BRICK. 


Wabash, 
Veedersburg, Ind. 


Mack Repressed, 
N. Cumberland, W. Va. 


PURINGTON, 

Galesburg, 111. 


Rattler loss, R 


Test. 
11.04 i 

3.07 


I 


II 


Ill 


Test. 
15.10 $ 

3.88 

3.40 j> 

4,190ft 

12,090ft 


I 


II 


Ill 


Test. 
14.34 i 

3.98 

1.12 $ 

3,380'ft 

13,220ft 


I 


II 


Ill 


Rattler loss In granite, 
R. G 






















3.26 


13.96 


41.80 


2.58 


9.90 


17.40 


2.51 


10.66 


22.00 


Absorption, A 


1.12 % 




Ratings 


0.22 


1.88 


23.50 


0.07 


-0.40 


14.40 


0.22 


1.88 


23.50 


Transverse, per Inch 
width, T 


3,8701b 






1.93 


3.87 


17.60 


2.09 


4.19 


19.00 


1.69 


3.38 


15.40 


Crushing, per square 
lnch,C 


12.490ft 




Ratings 


3.12 


3.12 


12.50 


3.02 


3.02 


12.10 


3.30 


3.30 


13.20 








Totals 




8.53 
100. 


22.83 
100. 


95.40 
100. 




7.76 
90. 


17.51 

77. 


62.90 
66. 




7.72 
89. 


19.22 

84. 


74.10 


Percentage ratings*.... 




78. 









•The •'Wabash" Is taken as the 



VITRIFIED PAVING BRICK. 



67 



The following seven brick were candidates for consideration 
by the city authorities, and after averaging the results of five 
tests on each brick the following ratings were calculated by 
formulae I, II and III, which are herewith shown side by side, 
in order to bring out their respective merits: 



1NGS OF FORMULAE I, II AND III. 



Terra Cotta Co. 
Galesburg, 111. 


MOBERLT, 

Moberly, Mo. 


St. Louis Press Brick 

Company. 

Glen Carbon, 111. 


Alton, 
Alton, 111. 


Test. 

19.78 * 

5.32 


I 


II 


Ill 


Test. 
16.42 i 

4.56 

1.56 jf 

3,530ft 

13,020ft 


I 


II 


Ill 


Test. 

19.75 $ 

5.11 
0.33 £ 

2,690ft 

13,190ft 


I 


II 


Ill 


Test. 

22.50 > 

7.37 
0.87 j 

2,570ft 

11,660ft 


I 


II 


Ill 
























0.64 

2,990ft 

14,650ft 


1.88 


5.22 


-10.70 


2.19 
0.16 


8.58 
1.44 


9.50 
21.80 


1.96 


5.25 


-10.50 


1.36 


2.50 


-27.00 


0.39 


2 36 


25.40 


0.75 


2.67 


26.70 
12.20 


0.29 


2.13 


24.50 


1.50 


3.00 


13.60 


1.76 


3.53 


16.00 


1.34 


2.69 


1.28 


2.57 


11.70 


3.66 


3.66 


14.70 


3.25 


3.25 


13 00 


3.30 


3.30 


13.20 


2.92 


2.92 


11.70 





7.43 
87. 


14.24 
62. 


42.00 
44. 




7.36 
86. 


16.80 
74. 


60.30 
63. 




7.35 

86. 


13.91 
61. 


41.60 
43. 




5.85 
69. 


10.1.2 
44. 


20.90 
22. 



unit for comparison, or as 100. 



Notes on the 
Brick. 



68 VITRIFIED PAVING BRICK. 

All of these brick are made from shale, except the "Mack," 
which is made from an impure fire clay. The "Wabash," 
"Mack," "Purington" and "Terra Cotta" brick are well known 
standard brands that have an excellent reputation and have 
been successfully used at many places. The "Moberly" is a 
local brick that is made from a superior shale, but the yard 
lacks kiln capacity, and the quality suffers in consequence. The 
"Glen Carbon" brick is made at a yard that was built for mak- 
ing press or building brick, which has recently attempted to 
make pavers; it uses the semi-dry process, and most of the 
kilns are open-top or up-draft, which permits only a small per- 
centage to be made as good as those used in the test. The 
"Alton" is a new yard that is still experimenting on different 
clay mixtures, with the hope of trying to improve the sadly 
deficient quality. 

Taking the "Wabash" as the unit, all the formulae agree in 
rating this as the best, and the "Alton" as the poorest; but for- 
mula I only finds a difference of 4 per cent, between the other 
five brick, though it is well known to the trade that there is a 
great difference between them, which is clearly shown by 
formula II, and still more keenly brought out by III. 

As granite blocks were used in the rattler test, the rattler 
losses are much greater than usual, or when only light scrap 
iron is used, and this does not give a fair idea of the brick as 
judged by formula III, if compared with usual rattler losses (or 
8.0 per cent.); but having all been made by the same expert in 
the sajne way, they are comparable with one another, and the 



VITRIFIED PAVING BRICK. 



69 



ratings of formula II or III satisfactorily bring out their rela- 
tive merits. 

USES OF VITRIFIED BRICK. 

In addition to the field for street paving, in which the cheap- 
ness and excellent quality of vitrified brick are going to make 
it a very formidable competitor of all other kinds of pavement, 
it has a special value for sewers, foundations, sidewalks, and 
chemical tanks. 

SEWERS.— Vitrified brick is exceptionally adapted for sew- 
ers on account of its low absorption, great strength and ex- 
treme hardness, and it has been adopted by St. Louis for this 
purpose. The latter quality will enable it to withstand the se- 
vere scouring action of sand, which rapidly wears out common 
brick if there is much velocity to the flowing water. Where the 
sewer grades will permit it, there is a bright future in the 
street-cleaning departments of our large cities when the vitri- 
fied brick is used for both the pavement and sewers, as then 
they can be thoroughly, rapidly and very cheaply cleaned by 
the hydraulic system. At present this is usually prohibitory, 
as the present soft brick in the sewers would cut out too 
quickly, necessitating the expense of frequent rebottoming, 
while macadam will not stand it, asphalt is injured (both 
chemically and mechanically), and granite, though free from 
these objections, needs too much water and the assistance of 
brooms, on account of its rough surface. Under the hydraulic 
system the work can be done with a small hose crew, by means 
of coal power at the waterworks, instead of with the present 



Street 
Cleaning. 



70 VITRIFIED PAVING BRICK. 

large gangs of men and teams, and the cleaning will be very 
much more thorough than with the present imperfect street- 
sweepers. The demand for this extra water for hydraulicing 
would be made at night, when there is only a small consump- 
tion of water for other purposes. 

FOUNDATIONS.— The low absorption and high crushing 
strength of vitrified brick make it an admirable material for 
foundations, especially in wet ground, for bridge piers or very 
high buildings. The heavy pressures that have to be sustained 
in the construction of the modern tall office buildings is espe- 
cially favorable for vitrified brick, as it is not only stronger 
and very much cheaper than granite, but it effectually keeps 
out dampness. If the brick are hammer-dressed or "rock- 
faced" they make a very ornamental front that is becoming 
quite popular. 

SIDEWALKS.— One of the earliest applications of vitrified 
brick was for sidewalks, as it is so very much more durable 
than the so-called "sidewalk" brick that are obtained from a 
building-brick kiln. The top course of pavers in a kiln are 
especially adapted for sidewalk use, as they are perfect in 
shape and free from kiln marks, and thoroughly vitrified. 
Their great strength enables them to be laid flat without dan- 
ger of breaking, which happens so frequently with common 
brick. 

CHEMICAL PURPOSES.— For lining vats or tanks for 
chemical purposes, vitrified brick is very valuable, as it is not 
attacked by acids or powerful chemicals, and so protects the 
tank from corrosion and the solutions from contamination. 



VITRIFIED PAVING BRICK. 71 

STREET PAVING.— There is a very large field for vitrified 
brick for paving in our cities, towns and county turnpikes 
which is only beginning to be occupied. It has so many ad- 
vantages, most prominent of which are low first cost and cheap 
maintenance, as to make it a very formidable rival to all other 
kinds of pavement, and to especially bring it within the means 
of small towns. With sufficient care in the manufacture, es- 
pecially in the annealing, a brick can be made and laid to 
stand the heaviest traffic of our large cities, while for the very 
much lighter traffic of the small cities and towns the cost of 
making and laying can be greatly reduced. 

COMPARISON OP STREET PAVING MATERIALS. 

A prominent but hasty criticism that is frequently made 
against paving brick is their want of uniformity. While care- 
lessness in manufacture and sorting may justify this, it should 
be remembered that this also holds true of all other pavements, 
as asphalt is very sensitive to the kind and manipulation of the 
materials that enter it; wood is very variable from decay, kind, 
age and position in tree; granite is eminently prone to weath- 
ering or softening, while the great variation in the hardness 
and durability of the macadam in St. Louis has cost it many 
friends. Of the different materials that are usually used for 
street paving— or cobble stones, macadam and telford, wood, 
asphalt, Belgian or stone blocks (usually granite), and brick— 
they will rate as follows in comparison with brick in the fac- 
tors that make up a good pavement: 

1. FIRST COST.— While local conditions greatly influence 
the relative costs, in most places in the United States brick is 
much cheaper than granite or asphalt, usually cheaper than 



72 VITRIFIED PAVING BRICK. 

telf ord and wood, excepting at the lake cities, but not usually 
as cheap as macadam or cobble stone, where the latter is to 
be had in local quarries or gravel banks. 

2. MAINTENANCE.*— The expense of repairs of good brick 
pavements, as determined from five to twenty-five years' ex- 
perience, is much lower than any other pavement, excepting 
granite, and is much superior in this respect to asphalt and 
macadam, its present chief rivals. 

3. TRACTION.— The ease of traction or haulage over brick, 
on account of the smoothness of the surface, exceeds that of 
any other pavement except asphalt, and Rudolph Hering 
gives the following relative estimate of the number of horses- 
required to haul the same load on the following pavements: 

Comparative Haulage of a Given Load on 

Iron rails 1 horse. 

Sheet asphalt 12-3 horses. 

Brick 2% to 2% horses. 

Granite blocks 3 1-3 to 5 horses. 

Wood 5 to G horses. 

Good macadam. 8 horses. 

Cobble stones : 7 to 13 horses. 

Ordinary earth 20 horses. 

Sandy earth 40 horses. 

4. FOOTING.— A sure, safe footing for horses and freedom 
from slipping is a very important requisite, which the joints of 

*The cost of repairs in St. Louis per annum has been lie 
per square for granite, 50c per square for wood, 50c per square 
for asphalt, 70c to $3.37 per square for macadam, and in one 
instance $9.40 where the traffic was heavy on limestone mac- 
adam. 



VITRIFIED PAVING BRICK. 73 

brick insure, especially if the edges are rounded. This is the 

very weak point of asphalt, in which it is greatly inferior to all 

other pavements, especially when sprinkled or on grades. 

Square-cornered bricks can be used up to 6 per cent., and with 

well-rounded corners up to 10 per cent., or as high as granite; 
for grades steeper than 10 per cent, cobble stone has the 

preference. 

5. DURABILITY.— The durability question is not only one 
Of cheap maintenance, but also the temporary loss of the use 
of the street during the reconstruction or resurfacing, and this 
is a very weak point in macadam, wood and asphalt, while 
brick is only exceeded by granite in this respect. Wood has 
been condemned in St. Louis, as it only lasts from two to 
seven years, and has proved very difficult to keep in good re- 
pair in the interim. 

6. CLEALINESS.— In the ease of keeping clean, brick 
stands second to asphalt, and if the hydraulic system is used, 
then it stands first, as the former will not successfully with- 
stand this thorough and cheap method of cleaning. 

7. REPAIRS. — Ease of repairs is important in cities, where 
the streets are constantly torn up to lay pipes, sewers, rails, 
wires, etc., and a city pavement should be elastic to permit 
this, without being seriously injured. Here cobble stones, brick 
and granite lead. 

8. HEALTH.— In the freedom from the lodgement of filth 
and decaying matter, which is a serious defect in cobble 
stones, stone blocks, wood and macadam, brick is only ex- 
ceeded by asphalt. 



74 



VITRIFIED PAVING BRICK. 



Blocks. 



Common Size. 



9. NOISE.— This is an important matter in cities, in which 
all the durable pavements are deficient. Wood is the ideal 
noiseless pavement, and the business men of London are will- 
ing to have their streets torn up every four to seven years to 
relay the short-lived wood, in order to get rid of the roar of 
heavy traffic on stone blocks. Macadam and telford are also 
very satisfactory as noiseless pavements, but they give too 
much trouble from dust and mud, unless maintained in an ideal 
condition of dampness that is very rarely realized, as they 
suffer as much from mud from so-called street sprinkling as 
from storms. Brick ranks next, as it is free from the sharp 
click of the horse's hoof that is so characteristic of asphalt. 
The dull, low rumble of stone blocks is only exceeded by the 
thundering of a lone, empty cart on a cobble stone pavement, 
which latter is so trying as to make it questionable whether 
the virgin dirt road, with its ills of mud and dust, is not more 
endurable to most of the citizens. 

SIZE OF BRICK.— When the manufacture of vitrified brick 
for paving first became an established industry, the brick- 
makers patterned their work after granite blocks. They soon 
found that it was very difficult to insure thoroughness and uni- 
formity in burning such large sizes, especially as the blunder 
was made, and to some extent is still perpetrated, of giving 
them an appearance of thorough vitrification by salt-glazing, 
and many brick pavements were justly condemned for the 
failure due to the soft brick that resulted. Against the pro- 
test of engineers, many manufacturers changed to the size of 
building brick, and the marked improvement in quality and 



VITRIFIED PAVING BRICK. 



75 



uniformity speaks for their good judgment, and has converted 
most engineers who have had much experience with paving 
brick. To-day the standard size is that, of building brick, or 
about 8^4x4x2% inches, and only a very small percentage (less 
than 10 per cent.) is made block size, or 9x4x3 inches or larger. 
There is a marked difference in the cost of making a standard 
and a block size brick, as the larger the size the greater the 
time and expense in drying and burning. There is a still 
greater difference in the market price, as the usual 25 per cent, 
of underburned brick can be sold to the building trade, if 
standard size, while there is practically no market for the soft 
blocks. Quality and cost, therefore, strongly emphasize the 
building brick size, while the reduced number of joints pre- 
sented by the large size does not give as good footing to the 
horses. 

Formerly brick were made with square or but slightly 
rounded corners, but the sharp corner soon chips off under 
wear, and until so chipped it makes a poor footing for the 
horses, on account of the tightness of the joints. Brick are 
now made with rounded corners, using a radius of one- 
quarter to three-eighths inch, which makes a more durable 
brick and furnishes a much better footing. Of the few blocks 
that are still on the market, several of them are patented, by 
having various shaped grooves pressed into their flat sides to 
assist in holding the tar or other filling employed, and of these 
the Hallwood patent is one of the best known, which is made 
by several concerns on a royalty. These grooves are not found 
necessary if the brick are laid on a good foundation, and their 



Rounded 
Corners. 



Grooves. 



76 



VITRIFIED PAVING BRICK. 



Concrete the 
Standard. 



Sand Cushion. 



value is greater as a trade-mark than for their intrinsic merit 
for paving purposes. 

FOUNDATIONS.— The success of any pavement depends 
primarily on a good foundation, and brick must have a good 
foundation if a smooth, durable pavement is desired. In the 
early experience of our brick pavements, the enthusiasm of the 
brick advocates went so far as to claim that brick would be 
satisfactory on any kind of a foundation, and very poor sup- 
ports such as sand, plank, etc.) were put under some of 
the early pavements, with the disappointing results that 
Avere bound to follow. Engineers have been quick to see this 
and insist on a good foundation, if a good pavement is desired, 
so that a concrete base is now the standard foundation. The 
concrete is made eight inches thick for heavy traffic, six inches 
for moderate, and four inches for very light traffic. Where the 
travel will not bear the expense of concrete, broken stone, 
gravel, or cinders have been substituted, thereby saving the ex- 
pense of the cement and mixing. A still cheaper foundation 
that has been largely used in the small cities and towns is to 
use a four to six-inch bed of sand, on which is laid a course of 
No. 2 pavers placed flatwise. Whether the foundation be con- 
crete, gravel or brick, a cushion of sand is always used be- 
tween it and the top course of brick, to take up the unevenness 
of the surface of the foundation and any irregularities in the 
brick. This sand cushion is usually two inches thick, but the 
writer thinks it should be reduced to one inch, as this is suffi- 
cient if the foundation is laid with care, and the thinner the 
cushion the less the risk of the brick settling or getting dis- 



VITRIFIED PAVING BRICK. 77 

placed in service. The top course of brick are laid on edge at 
right angles to the street, and at 45 degrees at intersections, 
and the joints between the brick are filled with cement grout- 
ing, tar, pitch or sand. A cement filling, if of Portland cement, Filling. 
binds the brick into a monolith, and gives the best results, as 
it is not affected by hot weather. Tar or pitch is also a good 
binder and filler, but it softens in hot weather, though this 
enables broken joints to 1 reunite, which is not the case with 
cement. In either case the grouting or tar should be thin when 
applied, so that it can penetrate into the joints, which are usu- 
ally only one-sixteenth to one-eighth inch wide. Sand filling is 
much cheaper, and permits the easy removal of the brick for 
pipe-laying, etc., and when once well worked in makes a solid 
pavement; but too frequently it is improperly applied by not 
having it perfectly dry and clean, when very little of it works 
into the cracks, no matter how persistently it is swept* over 
the surface. Before the filling is applied, the bricks are care- 
fully rolled to a true, uniform surface with a heavy roller, 
after which any broken or chipped brick are replaced, and after 
the pavement is finally thrown open to traffic a half-inch layer 
of sand is left on top for a month or so, to insure thorough 
filling of the joints. 

DURABILITY. — It is still premature to discuss the dura- 
bility of vitrified brick when properly made, as none of them 
have yet worn out, and the inferences deduced by experiments 



* Unless the sand is perfectly dry, it is better to flush it in 
with water, rather than attempt to work it in with a broom 
by sweeping. 



ments. 



78 VITRIFIED PAVING BRICK. 

made to determine this question are not satisfactory. In look- 
ing over the accumulation of evidence since brick were first 
used, twenty-five years ago, instances are not lacking where 
the brick have been unsatisfactory. An investigation of these 
failures invariably shows at least one of three causes, to- wit: 
bad foundation, soft brick or brittle brick. If the foundation 
Cause of Bad * s faulty any pavement will fail; for the soft or brittle brick 
Brick Pave= the manufacturer is primarily responsible in not properly 
handling his clay or not having a suitable clay (and the ma- 
jority of clays will not make a good paver); but lack of proper 
inspection is responsible for allowing such brick to be laid. 
The cupidity and short-sightedness of the brickmaker is not 
always responsible for bad brick going into pavements, as the 
opposition of interests in conflict with brick have in more than 
one instance purposely secured the worst brick, in order to kill 
off the threatening rival by making the first impression as un- 
favorable as possible — a mode of warfare by no means un- 
known in large cities. Like everything else, there are all 
grades of paving brick in the market, and it costs more to 
make a good article than a poor one; and if low first cost is 
the first consideration, and quality is secondary, inferior pave- 
ments will result, as a strictly first-class, hard, tough, care- 
fully selected brick cannot compete in price with soft, brittle 
and non-selected brick, though the former will make much the 
cheaper pavement when maintenance is considered. 

The experience of the oldest users of paving brick is here- 
with given, which also covers a broad range in the location, 
clays, size, foundation and price: 

The oldest brick pavement in use in this country is at 
Charleston, W. Va., where, after twenty-five years' serv- 



VITRIFIED PAVING BRICK. 79 

ice, the city engineer, Mr. W. A. Hogue, writes that it is now 
pretty well worn, after being 1 frequently torn up for laying 
pipes, and that it is a hard-burned building brick. 

Bloomington, 111., is now replacing a very poor, hard- 
burned, hand-made "slop" or building brick, after twenty years' 
service on a four-inch cinder foundation. 

Though both are small cities, these are remarkable records, 
considering the character of the brick, and strongly bespeak 
the durability of a thoroughly vitrified, annealed brick. 

Wheeling, W. Va., has been using fire clay brick for 
twelve years on six inches of gravel, and the city engineer, 
Mr. A. L. White, reports it in good condition. 

Galesburg, 111., has used vitrified shale brick for 
eleven years on its principal streets, which are still in excel- 
lent condition, though not a dollar has been spent in repairs, 
according to the city engineer, Mr. M. J. Blanding. 

Columbus, O.. has used brick for ten years, which are 
reported in good condition, with small repairs, by Mr. Josiah 
Kinnear, the chief engineer, 

Memphis. Tenn., has used brick for seven years with 
entire satisfaction and no repairs, per A. T. Bell, the city 
engineer. 

The engineering department of the C, B. & Q. railroad 
adopted vitrified shale brick for paving the Chicago freight 
yards three years ago, and it has proved so satisfactory under 
this very severe traffic that it was adopted last year for their 
very extensive new St. Louis freight yards. 

The writer is familiar with some hand-made fire clay blocks 
that were subjected to the heaviest traffic of St. Louis, or the 
entrance of the Missouri Pacific railroad freight yard, on 



80 



VITRIFIED PAVING BRICK. 



Seventh street, for seven years, with very favorable results, 
as the wear from the top surface amounted to only about one- 
quarter inch, yet these blocks were barely vitrified, and showed 
an absorption of 5.5 per cent of water in twenty-four hours. 

Experience of the Oldest 
As Reported by 



City 



Charleston n, W.Va 

Bloomington, 111. . 

Wheeling, W.Va 

Decatur, 111 

Galesburg, 111. . . 

Peoria, 111 

Columbus, Ohio 

Zanusville, Ohio 
Steubenville, Ohio 
Burlington, Iowa.. 

Parker sburg. W. Va 

Philadelptain, Pa.. 

Memphis, Tenn. .. 

Des Moines, Iowa . 

Omaha, Neb 

Cincinnati, Ohio. . . 
Detroit, Mich 

Louisville, Ky 

Indianapolis, Ind. 



Years 
Used. 



25 

20 

12 

12 

11 

10 

10 

10 

10 

8 

8 

7 

7 

7 

&A 

4 

5 

4 



p ?i pi i la " Traffic - 



12.000 

26,000 

3G,000 

27,000 

19,000 

60,000 

120,000 

30,OU0 
15,000 
30,000 

12,000 

1,300,000 

70,000 

80,000 
175,000 
225,000 
250,000 

205,000 

130,000 



Bus.* 

Bus. 

Bus. 

Bus. 

Bus. 

Bus. 

Bus. 

Bus. 
Bus. 
Bus. 

Bus. 

Res.f 

Bus. 

Bus. 
Bus. 
Res. 

Bus. 

Bus. 
Bus. 



Results. 



Very satis- 
factory 

Very satis- 
factory. 

Very satis- 
factory. 

Very satis 
facory. 

Very satis- 
factory. 

Very satis- 
factory. 

Satisfact'y 

Good. 

Satisfact'y 
Very satis- 
factory. 

Excellent 

Satisfact'y 

Very satis 
factory. 

Very satis- 

fact ry. 

Good. 

Fair. 

Fair. 

Very satis 
factory. 

Fair. 



Kind. 



rom.cl'y 

and shale 

Common 

clay 

Fire clay 

Common 
clay. 

Shale. 

Shale. 

Sh'leand 
fireclay. 

Shale. 

Fire clay 

Shale. 

Sh'leand 
fireclay. 

Sh'leand 
fireclay. 

Sh'leand 
fireclay. 

Shale. 

Shale. 

Shale. 
Sh'leand 
fireclay. 
Sh'leand 
fireclay. 
Sh'leand 
fireclay. 



Size. 



Brick. 

Br'k and 
block. 

Brick. 
Brick. 

Brick. 

Br'k and 
block. 

Block. 

Block. 
Brick. 
Brick. 

Block. 

Brick. 

Brick. 

Brick. 
Brick. 

Brick. 
Br'k and 

block. 
Br'k and 

block. 
Br'k and 

block. 



Used on business streets. 



VITRIFIED PAVING BRICK. 



81 



The following table gives additional information obtained 
by addressing - letters of inquiry to the city engineers of each 
place, and these cities were selected as giving the experience 
of the oldest users of paving brick: 



Large Ctties With Paving Brick 

the City Engineers. 



Fouuria- 
tiou. 



Boards. 
4" cinders. 
6" gravel. 
Flat brick. 

Flat brick 

6" concrete 
and gravel. 
8" b r o k e n 

stone. 
6"grav'land 

sand. 
Gravel. 

Flat brick. 



Repairs. 



Gravel and 
concrete 

7" to 8" cun 
crete. 

C>" concrete. 

6" concrete. 

6" coucrete. 

6" concrete. 

6" concrete. 

6" concrete. 



Slight. 
Slight. 

Slight. 

Very 

slight. 

None. 

Slight. 

Slight. 

Slight. 

None. 
Very 

slight. 
Very 

slight. 

Usual. 

None. 

None. 
Slight. 
Slight. 
Slight. 

None. 

None. 



Cost Per 
Sq. Yd. 



Remarks. 



Will stand heavy traffic. 

$1.25 Will stand heavy traffic 

)0 Will stand heavy traffic 

50 Will stand heavy traffic 

J8 Will stand heavy traffic 

1.40 to 1.60 Have over 70 miles. 
I 
.75 to 1.50 Will stand heavy traffic, 



.67 to 


1 19] 


.78 to 


.89 




2.05 




285 


1.30 to 


1.50 


1.40 to 2.09 




1.70 


1.60 to 


1.80 


1.50 to 


1.80 


1.50 to 


1.60 



Will stand heavy tr a 



Will stand heavy traffic 
Will stand heavy traffic. 



Will not stand heavy 

traffic. 
Will stand heavy traffi •. 

Will stand heavy traffic. 



Authority. 



W. A. Hogue. 

W. P. Butler. 

A. L. White. 

G. V. Loring. 

M. J. Blanding. 

A. D. Thompson 

Josiah Kiunear. 

A. E. Howell. 
J. M. I arclay. 
Wm. Steyh. 

J. S A. Farrow. 

G. A.Bullcck. 

A.T. Bell. 

F.^elton. 
A. Rosewater. 

H.D. Ludden. 
C. V. Mehler. 
C. C. Brown. 



t Used on residence streets. 



82 



VITRIFIED PAVING BRICK. 



First Year's 
Wear. 



The Future of 
Paving Brick. 



The record of these cities and towns, which conld have been 
largely increased if desired, shows conclusively that brick is 
very durable under traffic as heavy as is found in cities of 
25,000 to 200,000, and inexpensive to maintain. In the very 
large cities, brick has thus far been largely confined to residence 
or other streets where the traffic is not very heavy, though the 
experience of the Chicago and St. Louis freight yards shows 
that this conservatism is unnecessary, and that first-class brick 
can be safely exposed to the severest traffic with satisfactory 
results. In examining the wear on a brick street, the first year's 
traffic is the crucial one, as the brittle and soft brick will show- 
in that time; after that the wear is very small, and a con- 
tractor who lays a first-class article need have little to fear 
with five or ten-year maintenance clauses, which are now being 
so largely and wisely adopted in municipal work. 

In view of the fact that a marked improvement has been 
made in the past five years in the quality of paving brick by 
tising better kilns and dryers, repressing, and more careful 
manipulation of the clay, which has resulted in a more uniform 
as well as a better brick, it is safe to say that the superior 
grades of brick now being manufactured will prove much more 
durable than those made previous to 1890. Even now we oc- 
casionally get results in the rattler that show greater dura- 
bility than granite, while if the clay is ground finer, more thor- 
oughly pugged, forced out of the machine in sounder bars, 
more carefully burned (with oil or gas if possible), and very 
slowly annealed, the writer has no hesitancy in saying that the 
brick resulting therefrom, when carefully selected, will be 



VITRIFIED PAVING BRICK. 83 

perfectly able to withstand the severest traffic of our largest 
cities, and to safely replace the present noisy, rough, high-trac- 
tion granite blocks. But this improved brick will cost more to 
make, and can never be profitably placed on the market if en- 
gineers are going to permit the lowest bidder to secure the 
work and allow quality to be made a side issue. Such a su- 
perior brick is already in sight, and within the reach of those 
who wish the best and most economical article for paving. 

COST. — The cost of vitrified brick pavements varies greatly, 
according to the foundation used, quality of the brick em- 
ployed and distance from the point of manufacture. The cost 
of good vitrified brick ranges from $8 to $10 for nnrepressed, 
and $9 to $12 per 1,000 for repressed brick at the kiln; inferior 
brick shade this by $1 to $2. Freight brings the price up 
rapidly, as 1,000 brick will range from 5,500 to 7,500 pounds, 
according to size and quality. In the St. Louis market inferior 
brick sell for $10 to $11, and first-class brick for $11.50 to $13 
this season (1895). Alley contracts were let in St. Louis* this 
season at $1.30 to $1.40 per square yard, using a six-inch con- 
crete foundation, one-and-one-half -inch sand cushion and cement, 
grouting, but inferior brick were used. 



* Street contracts in St. Louis were let this year (1895) at the 

following rates per square, or 100 square feet: 

Brick, on six-inch concrete $14.50 to $15.00 

Asphalt, on six-inch concrete 26.00 to 30.00 

Granite, on six-inch concrete 20.00 to 25.00 

Granite, on sand 16.00 to 20.00 

Common telford, fifteen inches deep. 10.00 to 12.00 
Improved telford, twenty inches deep 16.00 to 18.00 
No wood will be laid, as this has been condemned by the 

Board of Public Improvements. 



84 VITRIFIED PAVING BRICK, 

Wheeling gets about the cheapest rates, being in the heart 
of the clay fields, and fire clay brick on a six-inch rolled gravel 
foundation, two-inch sand cushion and sand filling cost only $1 
per square yard, including grading. 

Zanesville, O., with brickyards in the city, has laid brick 
on only a two-inch sand bed for 75 cents, but usually uses 
six inches of rolled gravel, when it costs $1.30 to $1.50. 

At Indianapolis, AVith six-inch concrete, it costs $1.80, and 
$1.50 to $1.60 with broken stone, with a five-year maintenance 
agreement. 

At Peoria, 111., where only first-class brick are accepted, 
brick on six inches concrete cost $1.50 last year, and $1.25 to 
$1.35 this year (1895). 

At Bloomington, 111., on a four-inch rolled cinder base and 
sand cushion, it costs only $1.25 for shale brick. 

At Galesburg, 111., the home of shale paving brick, it costs 
$1.35 to $1.60, laid on a course of flat brick. 

At Des Moines, la., with several factories in town, it costs 
$1.30 to $1.50 on six inches concrete. 

At Washington, D. C, they have only been used for alleys, 
as brick pavement costs more than asphalt, and the traffic is 
so very light that asphalt is quite durable. 

At Philadelphia, Pa., on concrete base, it costs $2.05. 



Books for... 

== ^ 

Brickmakers. 



IT IS pretty generally conceded that wonderful progress is 
being made in the ancient and heretofore unprogressive 
art of brickmaking. Among the best evidences of this is the 
fact that the brickmaking craft is no longer without a litera- 
ture of its own. There are now some good practical books 
treating on the manipulation of clay — the making, drying and 
burning of brick. The list is not so large but that every brick- 
maker can afford to have them all. Get them and read them. 

"BRICKMAKER'S MANUAL," 

Morrison and Keep, $3.00 
"BRICKMAKING AND BURNING," 

- J. W. Crary, Sr., $2.50 
"TABLE OF ANALYSES OF CLAYS," 

Alfred Crossley, $1.00 
"VITRIFIED PAVING BRICK," 

H. A. Wheeler, E. M., $1.00 

Mailed, postage free, on receipt of price. Address 

T. A. Randall & Co., Indianapolis, Ind. 

We also fill orders for the English work enti- 
tled "THE MANUFACTURE OF GLAZED 
BRICK," H. Greyville Montgomery, $2.00. 






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